Work Text:
The library coffee machine had been broken for three days straight. Severus Snape stared at it like it had personally betrayed him, fingers twitching around his empty mug. Across the room, Lily Evans stifled a laugh into her textbook.
"You could just ask the staff to fix it," she said, nudging his shoulder. Severus didn't budge. "Or, I don't know, go to the café like a normal person."
"Normal people waste fifteen minutes in line for burnt espresso," he muttered, still glaring at the machine. "This was efficient."
Lily rolled her eyes and stretched her legs under the table, accidentally kicking his shin. Severus didn’t even flinch. "You’re impossible," she sighed, then paused as her gaze flickered over his shoulder. A slow smirk curled her lips. "But maybe you won’t have to suffer much longer. Help’s arrived."
Before Severus could turn, a familiar voice cut through the hum of study chatter. "Oi, Snape. Heard you’ve been staring down appliances like they owe you money." Sirius Black slid into the seat beside him, close enough that their elbows brushed. Too close. Severus stiffened but didn’t move away—which Lily noted with raised eyebrows.
Sirius pushed a steaming takeaway cup toward him. "Double shot, black. Figured you’d be crawling up the walls by now." He grinned, sharp and effortless, like he hadn’t just crossed campus in the rain for no apparent reason.
Severus stared at the coffee, then at Sirius’s damp sleeves. "How did you—"
"Lucky guess," Sirius said breezily, leaning back. His knee knocked against Severus’s under the table. Neither of them corrected it.
Lily coughed pointedly into her fist. Severus ignored her, but his fingers tightened around the cup.
Sirius popped his chin on his hand. His thumb swiped a drop of condensation off the cup lid, slow and deliberate. Severus watched the motion like it was a puzzle he couldn’t solve.
Lily kicked him again—harder this time. When he finally glanced at her, she mouthed, Are you kidding me? Severus frowned.
Sirius, oblivious or willfully ignoring them both, stretched his arm across the back of Severus’s chair. "So," he said, "you gonna drink that or let it go cold too?"
Severus blinked. "It’s still hot." He lifted the cup, inhaling the bitter aroma before taking a sip. Perfect. Exactly how he liked it. Which was—odd. Sirius shouldn’t know that. "Why did you—"
"Merlin’s saggy left tit," Lily muttered under her breath, snapping her textbook shut with unnecessary force. "Sirius, don’t you have, I dunno, a class? A dog to walk? A prank to plan?" She flapped her hands in a shooing motion. Sirius grinned, unbothered, but finally—finally—stood up, his fingers lingering on the back of Severus’s chair for a beat too long.
"Later, Snape." He winked—actually winked—and sauntered off, whistling.
The second Sirius was out of earshot, Lily whirled on Severus. "You cannot be serious."
He sipped his coffee again, savoring the heat. "About what?"
She groaned, dragging her hands down her face. "Okay. I see we will need to do this doing step by step." She grabbed a fresh sheet of parchment and scribbled FLIRTING: across the top in bold letters.
Severus eyed it with mild distaste. "Lily, I have a lecture in twenty minutes."
She jabbed her quill toward the parchment. "First lesson: proximity." Scanning the library, she pointed at a couple two tables over—a Hufflepuff girl practically sitting in her boyfriend’s lap. "See that? Personal space invasion is Flirting 101.
Severus glanced at the couple, then at the empty seat Sirius had vacated. "That’s just poor spatial awareness."
Lily sighed and drew a crude stick figure leaning into another stick figure’s bubble. "No. It’s intentional. Like when someone"—she tapped the parchment—"finds excuses to touch you. Casual brushes, lingering hands." She smirked as Severus’s fingers twitched around his cup.
He scowled.
"Second lesson," she plowed on, nodding toward a pair by the window. The Ravenclaw boy kept tucking his hair behind his ear, laughing too loudly at his companion’s jokes. "Mirroring. People subconsciously mimic the person they’re into. Leaning in when they lean, laughing at terrible puns—"
Severus squinted at them. "Or he has auditory processing issues and needs to face her directly to hear properly."
Lily's quill snapped in half. She inhaled sharply through her nose and flipped the parchment over, sketching a new diagram with unnecessary force. "Fine. Lesson three: unnecessary favors." She gestured to a Gryffindor boy across the aisle handing his crush a stack of freshly sharpened quills. "Going out of one's way to provide unasked-for assistance—"
"Or," Severus cut in, watching the girl pocket the quills without looking up from her essay, "he's compensating for snapping hers last week."
Lily exhaled through clenched teeth and stabbed the parchment so hard the nib tore through. A Slytherin couple near the restricted section saved her—the boy casually draping his robe over his girlfriend's shoulders. "Gift-giving. Offering something personal—"
"Temperature," Severus said without looking up. "Her sleeves are sheer. The library is drafty."
Lily fought the urge to headbutt the table, just barely. Instead, she dug her nails into the wood and exhaled through her nose like a dragon gearing up to torch a village.
"Right," she muttered, crumpling the failed diagrams into her bag with unnecessary violence. "We’re upgrading to live demonstrations."
Before Severus could protest, she hauled him up by his sleeve—ignoring his indignant squawk—and dragged him toward the nearest alcove where a pair of Ravenclaws were whispering behind a potted fern.
"Observe," Lily hissed, shoving him behind a bookshelf. The taller Ravenclaw—a wiry boy with ink-stained fingers—was leaning so far into his companion’s space that his nose practically brushed her temple. "See how he’s angled his entire torso toward her? That’s textbook—"
Severus squinted. "Or he’s compensating for the shelf behind him digging into his spine."
Lily made a sound halfway between a groan and a scream, muffling it into her palms. Clearly this was going to take some time. Maybe centuries. Maybe the death of the universe would arrive before Severus Snape recognized a blatant come-on if it hexed him in the face. She exhaled sharply, counted to three in her head, and decided radical measures were necessary.
A few days later, they were crammed into a booth at the Three Broomsticks—James slinging an arm around her shoulders, Remus nursing a butterbeer, Peter already three crisps into oblivion—and Sirius Black was dressed like sin incarnate. The deep V of his leather jacket plunged to his navel, his rings glinted with every languid gesture, and his knee kept brushing Severus’s under the table like he was trying to start a fire.
Severus, meanwhile, was dissecting a charmed napkin like it held the secrets of the universe, entirely unfazed by the fact that Sirius had just licked butterbeer foam off his own wrist with deliberate, unhurried precision. Lily watched, jaw slack, as Sirius stretched—slow, feline—arching his back just enough to make his shirt ride up. Severus glanced over, frowned, and muttered, "Posture like that’ll wreck your spine by thirty."
James choked on his firewhisky. Remus buried his face in his hands. Peter, bless him, just blinked and reached for another crisp.
Lily kicked Severus under the table. Hard. He shot her a glare, but she just gestured wildly at Sirius, who was now leaning so far forward his jacket gaped wider, revealing a silver chain nestled against his collarbones. Severus followed her pointed stare—lingered for half a second—then shrugged. "What? It’s drafty in here."
Sirius grinned, slow and wicked, and deliberately tapped his foot against Severus’s ankle. "You cold, Snape? I could lend you my jacket." He shrugged it off one shoulder, letting it slide down his arm with exaggerated slowness.
Severus eyed the offered leather like it might bite. "Unnecessary. I’m adequately dressed."
Lily groaned and slumped against James, who was shaking with silent laughter. "I give up," she muttered into his shoulder.
Sirius, undeterred, tilted his head, letting his hair fall artfully over one eye. "Suit yourself," he purred, draping the jacket over the back of Severus’s chair instead—close enough that the scent of cedar and something smokey clung to the air between them.
Severus sniffed. "Your cologne is overpowering."
Remus made a noise like a dying teakettle. Peter patted his back sympathetically.
James, ever helpful, leaned in. "Mate," he stage-whispered to Severus, "if someone dressed like that handed me their clothes, I’d—"
"Develop a rash, presumably," Severus cut in, sipping his drink. "Polyester allergies are common."
Lily stared at the ceiling like it might offer divine intervention. Sirius, meanwhile, just laughed—bright and unbothered.
Severus blinked. "It's statistically improbable."
Lily made a strangled noise.
Sirius leaned forward, resting his chin on his palm, fingers drumming lazily against his cheekbone. "What is?"
"The likelihood that you guessed my coffee preference correctly," Severus said flatly. "Assuming you didn’t stalk my habits—which would be concerning—the probability is approximately one in—"
"Fourteen," Sirius interrupted, grinning. "Fourteen standard coffee orders at the café. Eliminated the sweet ones immediately—you’d rather chew glass—then factored in how you hold your mug when it’s too weak. You curl your fingers tighter. Like this." He mimicked the motion, his long fingers flexing. Severus stared at them, brow furrowing.
"That’s—" He paused. "Unnecessarily observant."
Sirius winked. "Just for you, baby."
Severus opened his mouth—closed it. Lily seized the arm and pulled him through the noisy bar to the toilets.
"This is the ladies bathroom, Lily."
"Shut up," Lily hissed, shoving him against the sink and locking the door with a flick of her wand. The floral-scented air was thick with the ghosts of perfume and spilled cocktails. She whirled on him, hands braced on either side of the porcelain. "Are you trying to drive me to homicide?"
Severus adjusted his sleeve where her grip had wrinkled it. "Your question is hyperbolic. You lack both motive and—"
"—Oh my god." Lily pressed her palms to her temples as if physically restraining her patience. "Severus. He brought you coffee. Memorised how you hold your mug. Leans into your space like a human fucking limpet. And you think—what? That's normal friendship behavior?"
Severus blinked at her, utterly unruffled. "I wouldn't know. Sirius and I are not friends." He said it the way one might remark on the weather—a simple, immutable fact. "Therefore, I have no baseline for his 'normal friendship behavior.' If he behaves similarly with Potter or Lupin, then statistically, this is likely just—"
Lily's hands shot out, gripping his shoulders as if she could physically shake sense into him. "Severus. Listen to me. Sirius does not do this with James. Or Remus. Or anyone." Her voice dropped to a furious whisper. "He once transfigured James' shoelaces into snakes for borrowing his quill without asking. But for you? He walked across campus in the rain. With precision-brewed coffee."
Severus frowned, processing. "That's inefficient. The café is in the opposite direction from his dormitory."
Lily made a strangled noise. "That's the point—"
Severus cut her off with a precise hand gesture, his fingers flicking outward like he was dismissing an illogical hypothesis. "No. If Sirius wanted efficiency, he would have waited for the coffee machine repair. Or gone to the nearest café. Walking fifteen minutes in inclement weather for a beverage that could be acquired in three is objectively irrational." He paused, then added clinically, "Unless he enjoys precipitation. Which seems unlikely, given his hair-care regimen."
Lily gaped at him, her fingers twitching like she wanted to throttle the sink instead. "Severus. Sweetheart. Light of my godforsaken life." She inhaled sharply through her nose. "People do irrational things when they like someone. That's the entire premise of flirting."
Severus tilted his head slightly, his dark eyes narrowing in genuine confusion. "But why? Flirting, by definition, is a courtship behavior aimed at increasing reproductive success. Spending excess time and resources on trivialities decreases efficiency, thereby undermining the evolutionary advantage." He frowned. "Unless the display of resource expenditure is itself the signal—like peacocks with plumage. But Sirius isn't presenting me with a carcass."
Lily's eyelid twitched. "Okay. New angle." She grabbed his hands, pressing their palms together with exaggerated slowness. "Do you like when Sirius does these things? The coffee. The... leaning. The—Merlin help me—winking?"
Severus blinked down at their joined hands, then back up at her. "Like is a subjective term. His coffee is adequately prepared. His spatial awareness is concerning but not actively detrimental to my workflow. The winking is statistically anomalous but harmless." A pause. Then, quieter: "I don't dislike it."
Lily exhaled so hard her bangs fluttered. "Progress." She released his hands to grip the sink again, knuckles whitening. "Severus," she said slowly, "remember last winter when I knitted you those atrocious green mittens?"
Severus's expression flickered—something almost fond beneath the perpetual neutrality. "They were impractical. Wool retains moisture, reducing thermal efficiency."
"Yes," Lily pressed, "but you wore them every damn day until they unraveled."
"That's—" Severus hesitated, fingers twitching at his sides as if physically grasping for logic. "Different. You have... baseline competence in fiber arts. The mittens were serviceable."
Lily arched a brow. "And when James 'accidentally' set them on fire with that stupid charm?"
Severus's jaw tightened imperceptibly. "An isolated incident."
"You hexed him into next week," Lily deadpanned. "Point is—you liked them because they were from me. Not because they were logical."
Severus opened his mouth—closed it. Somewhere beyond the bathroom door, Sirius's laughter rang out, bright and reckless. Severus's gaze flicked toward the sound before he forcibly straightened his shoulders.
"Hypothetically," he said, painfully deliberate, "if Sirius's actions were... motivated by non-utilitarian factors..."
Lily nearly wept. "Yes?"
Severus studied a chip in the sink's enamel. "How would one... reciprocate?"
Lily's grin could have powered Hogwarts for a year. "Oh, Sev." She patted his cheek. "Okay, we're starting with eye contact."
Severus recoiled. "Unnecessary. Visual processing is—"
"—Vital," Lily interrupted, dragging him toward the mirror. "Look. When he's talking, hold his gaze for three seconds. Then look at his nose if it's too much."
Severus glared at his own reflection like it had insulted his potions textbook. "This is ridiculous."
"So is chemistry," Lily shot back, "but you still memorise every damn reaction."
A beat. Then, grudgingly, Severus practiced—blinking rapidly like an owl adjusting to sunlight.
Lily muffled a laugh in her sleeve. "Perfect. Next lesson: compliments."
Severus looked vaguely ill.
"Start small," Lily said, steering him toward the door. "Tell him his... I dunno, his boots are adequately polished."
Severus paused, hand on the doorknob. "...They are."
Lily beamed. "There you go."
Beyond the door, Sirius's voice curled around another joke, warm and inviting. Severus inhaled sharply—then stepped forward.
Lily crossed her fingers behind his back.
Severus strode back to the booth like a man marching toward a duel—shoulders rigid, gaze fixed dead ahead. Sirius was mid-laugh when Severus stopped abruptly beside him, fists clenched at his sides. The table fell silent. Even Peter paused mid-crisp.
Severus inhaled sharply. "Your boots," he announced, voice flat as a textbook diagram, "are adequately polished."
Sirius blinked. Remus choked into his butterbeer. James wheezed like a deflating whoopee cushion.
Sirius glanced down at his scuffed dragonhide boots—clearly unpolished for weeks—then back up at Severus with slow, dawning delight. "Yeah?" He stretched his legs out, knocking their ankles together. "You like 'em?"
Severus frowned. "I stated a fact."
Lily kicked him under the table. Hard.
Severus cleared his throat. "They are... functional," he amended stiffly. "And aesthetically... sufficient."
Sirius's grin widened. "Sufficient, huh?" He leaned forward, resting his chin on his palm—deliberately mirroring Severus's habitual thinking pose. "What else d'you find... sufficient, Snape?"
Severus's ears pinked. He locked eyes with Sirius—precisely three seconds, as instructed—then abruptly shifted focus to Sirius's left eyebrow. "Your... hair." Pause. "It is... clean."
James face-planted into the table. Remus muttered, "Merlin save us."
Sirius, however, looked positively giddy. He shook his head, sending his dark locks tumbling artfully over one eye. "Clean, eh?" He twirled a strand around his finger. "Washed it just for you."
Severus blinked. "That's illogical. Hair hygiene is a personal health necessity, not a—"
Lily stomped on his foot.
Severus exhaled sharply through his nose. "...Thank you," he ground out, like the words physically pained him.
Sirius's smirk softened at the edges. He nudged his untouched butterbeer toward him. "You're welcome," he said, quiet enough that only Severus heard—and Lily, who was leaning so far forward she was practically in James's lap.
Severus stared at the drink. Then, with agonizing deliberation, he picked it up, took a sip—and handed it back to Sirius. Their fingers brushed. Neither pulled away.
"Sufficient," Severus muttered.
Sirius's grin could've lit up the Forbidden Forest. "High praise," he teased, but his thumb stroked the condensation on the glass exactly where Severus's lips had been.
Lily collapsed against James, exhausted. "Thank, Merlin," she mouthed to the ceiling.
"Alright, next one," Lily whispered urgently, nudging him with her elbow. "Physical contact."
Severus frowned. "I don't see how unnecessary tactile interaction—"
"—Just tap his wrist when you disagree with him," Lily interrupted, pinching the bridge of her nose. "Like this." She demonstrated by brushing her fingers against his sleeve. Severus stared at the spot as if it might spontaneously combust.
Sirius, meanwhile, was mid-rant about Muggle motorcycles, gesturing wildly with his butterbeer. "—and the torque on a '69 Bonneville could outmaneuver a Hungarian Horntail—"
"False," Severus said automatically. Then, remembering Lily's instruction, he reached out and tapped Sirius's wrist—once, precisely, like he was calibrating a delicate instrument.
Sirius froze mid-sentence, his arm still suspended in the air. His skin was warm beneath Severus's fingertips.
Severus blinked. "The Horntail's wingspan allows for a tighter turn radius than any combustion-engine vehicle," he continued, matter-of-fact, but his fingers lingered a half-second too long before retreating.
Sirius's throat bobbed. He set his drink down carefully, as if handling glass. "Yeah?" he rasped, leaning in. "Prove it."
Severus opened his mouth—closed it. Lily's whispered instructions hadn't covered this scenario. He defaulted to staring at Sirius's left eyebrow again.
"Draw me a diagram," Sirius goaded, sliding a napkin toward him. His grin was all teeth.
Severus exhaled sharply through his nose and grabbed the nearest quill. He sketched two precise arcs—dragon wingspan versus wheelbase—his shoulder pressing against Sirius's as he hunched over the napkin.
Sirius didn't move away.
"See?" Severus said, pointing at the calculations. "The angular velocity alone—"
"—Mm," Sirius agreed, but he wasn't looking at the diagram. His gaze was fixed on Severus's mouth.
Lily kicked James under the table, her eyes wide. James mouthed, Holy shit.
Severus, oblivious, tapped the napkin again. "The numbers don't lie."
"Neither do I," Sirius murmured, shifting closer until their thighs pressed together under the table. "About liking you."
Severus's quill snapped.
A beat of silence. Then, with clinical precision: "That's... statistically unlikely."
Sirius laughed—bright, startled—and curled his fingers around Severus's ink-stained ones. "Try me."
Severus stared at their joined hands. Lily held her breath.
"...Your hypothesis," Severus said slowly, "requires further testing." Before turning to Lily, "I suppose this is were physical contact comes into play?"
Sirius barked a laugh, squeezing Severus's fingers. "Christ, Snape. You're supposed to feel things, not dissect them."
Severus blinked. "Tactile input is processed by the somatosensory cortex. Of course I feel it." He flexed his fingers experimentally against Sirius's palm. "Your callouses suggest frequent broom use, but the scarring pattern indicates—"
"—Merlin's tits," Sirius groaned, but he was grinning as he laced their fingers together properly. "Just tell me if you like it or not."
Severus considered this. "The pressure is adequate. Your skin temperature runs approximately 1.2 degrees higher than average, which—"
Lily facepalmed so hard it echoed.
"—is not unpleasant," Severus finished. His thumb brushed Sirius's knuckles once, twice—mechanical at first, then lingering. "Your vascular response suggests increased cardiac output. Are you unwell?"
Sirius's grin turned feral. "Oh, I'm very well." He leaned in until his breath ghosted Severus's cheek. "Your turn. Tell me what you want."
Severus's gaze flicked to Lily, seeking confirmation. She mimed kissing so aggressively James had to grab her wrists.
"Ah." Severus nodded, then turned back to Sirius with academic precision. "I hypothesize mutual romantic interest would be most efficiently confirmed via direct physical—"
Sirius kissed him. Hard.
Severus froze—hands suspended mid-air like a startled cat—before slowly, painfully deliberately placing them on Sirius's waist. When they broke apart, he looked mildly astonished. "Hmm. Dopamine release was... significant."
Sirius was flushed, breathing ragged. "Yeah? Wanna run more tests?"
Severus studied him with newfound intensity. "Extensive replication is necessary for verifiable results." Then he yanked Sirius forward and kissed him.
James wolf-whistled. Remus covered Peter's eyes. Lily burst into tears.
"Methodology seems sound," Severus murmured against Sirius's mouth, fingers tangling in leather. "Though your breathing patterns are concerning."
Sirius laughed, wild and bright. "Sweetheart, you're gonna kill me."
Severus frowned. "Unlikely. Your carotid pulse is—"
Sirius kissed him again. Harder.
********
Severus's morning coffee was now a ritual—Sirius brought it precisely at 8:17 AM, black with two sugar cubes (Statistically optimal for neural stimulation," Severus had declared after three weeks of data collection).
"Morning," Lily yawned, sliding into her usual seat in the library. Severus didn't look up from his parchment, where he was graphing something in violent purple ink.
"Fascinating," he said, shoving the paper toward her. "Sirius's resting heart rate increases by 12.3% when I—"
Lily slapped a hand over the chart. "No. No more cardiovascular data. I'm begging you."
Severus blinked. "You insisted I document my findings."
"Yes, emotional findings! Not—" She peeked at the parchment and recoiled. "Is that a scatter plot of his moans?!"
"Correlation doesn't imply causation," Severus said gravely. "But the data suggests—"
"Stop." Lily pressed her forehead to the table. "Just say 'he's cute' like a normal person."
Severus considered this. "His epidermal temperature fluctuation patterns are aesthetically pleasing."
Lily groaned.
Later, Sirius slung an arm around Severus in the common room, nuzzling his neck. Severus tilted his head like a biologist observing a fascinating specimen. "Your salivary pH is unusually alkaline today."
Sirius grinned. "Yeah? Wanna taste?"
Lily, passing by with a stack of books, hissed, "Don't answer that."
Too late. Severus nodded. "For science."
Sirius's grin widened as he pulled Severus onto his lap—and Lily promptly dropped her books. "Nononono—"
Severus licked a stripe up Sirius's throat with clinical precision. "Saliva viscosity is consistent with prior samples," he mused, then frowned. "Though electrolyte composition suggests mild dehydration. Have you consumed adequate fluids today?"
Sirius, now flushed and breathing unevenly, managed a strangled, "Fuck fluids—"
"Language," Severus chided, pressing two fingers to Sirius's carotid. "Elevated pulse. Pupillary dilation." He leaned closer, nose brushing Sirius's cheekbone. "Respiratory rate indicates—"
Lily tackled a pillow over her face. "I regret every life choice that led me here."
"—overstimulation," Severus finished, clinically detached even as Sirius groaned and arched against him. "Interesting. Would you describe this as pleasurable or—"
"Yes," Sirius hissed, fingers digging into Severus's hips.
Severus nodded, making a mental note—Lily heard the mental note—before turning to her. "Fascinating. The correlation between tactile stimulation and vocalisation frequency is—"
"Nope!" Lily vaulted over the couch. "Boundaries! Remember our talk about boundaries?!"
Severus blinked. "You said sharing findings promotes emotional intimacy."
"Not these findings!" She gestured wildly at Sirius, who was now mouthing at Severus's collarbone with single-minded devotion. "Especially not with diagrams—why is there a diagram?!"
Severus calmly unrolled a parchment titled Fig. 1: Oral Stimulation Efficiency (N=47 trials). As you can see, the angle of—"
Lily set the parchment on fire.
Sirius whimpered. "That was aminated."
Severus eyed the ashes. "Statistically, your pyromania peaks during discussions of my research." He pulled out a backup copy. "As I was saying—"
Sirius winked. "He is good at angles."
Lily choked on her tea, spraying Earl Grey across the library table. "I said keep that to yourself!"
Severus, utterly unperturbed, tapped his quill against a parchment titled Fig. 3: Optimal Fellatio Trajectory (N=82 Trials). "Your reaction is inconsistent. You previously emphasised the importance of 'communicating needs'—"
"I meant romantic needs! Not—" Lily gestured wildly at the diagram, where a disturbingly detailed stick figure was annotated with phrases like "maximal glans stimulation at 34 degrees."
Sirius smirked against Severus’s neck. "Thirty-four exactly. He used a protractor."
Severus adjusted his notes. "Margin of error: ±1.5 degrees. Your mandible exhibits impressive flexibility."
Lily slammed her hands over her ears. "STOP."
Sirius only laughed, nuzzling Severus’s ink-stained fingers. "Tell her about the moan frequency study."
Severus brightened. "Ah! Vocalizations peak at 87 decibels during—"
"NO—"
"—scapular contact," he finished, blinking at Lily’s horrified expression. "You’re hyperventilating. Should I fetch water?"
Sirius nipped his earlobe. "Let me demonstrate Fig. 4?"
Severus straightened his collar with academic severity. "Unnecessary. The refractory period data is conclusive—"
"—I'll be quick," Sirius purred, fingers already working at Severus's belt.
Lily threw a textbook at them. It bounced off Severus's shoulder; he caught it midair without breaking eye contact with Sirius. "Impact velocity suggests heightened emotional distress," he noted clinically. "Lily, your systolic pressure must be—"
"—OUT!" Lily shrieked, pointing at the door with a shaking finger.
Severus blinked. "The library closes at midnight. It's currently—"
Sirius licked a slow stripe up Severus's neck. "Wanna test the echo in the Restricted Section?"
"Fascinating." Severus stood abruptly, dragging Sirius up by his scarf. "The stone arches there could amplify vocalizations by 30% based on architectural—"
Lily tackled them both into a shelf. Ancient tomes rained down as she hissed, "If I hear one more decibel reading, I swear I'll—"
"—but you encouraged data collection," Severus protested, extracting himself from under Sirius (who was grinning like a man who'd won the Quidditch World Cup). "You said 'healthy relationships require communication.'"
"NOT GRAPHS!" Lily jabbed a finger at the latest parchment unfurling from Severus's sleeve—Fig. 5: Seminal Fluid Volume (N=12 Ejaculations)—and promptly set it aflame.
Sirius pouted. "He worked hard on that."
Severus shrugged, adjusting his collar. "I have backups. And your salivary consistency correlates positively with hydration levels post-coitus, so—"
Lily clamped her hands over her ears. "NO POST-COITAL ANALYSIS IN THE LIBRARY!"
Severus tilted his head. "Then where would you prefer we discuss—"
"NOWHERE!" Lily shrieked, flinging a quill at them. It lodged in Sirius’s hair like a wayward porcupine spine.
Severus plucked it out with clinical precision. "Fascinating. The tensile strength of Black family hair follicles exceeds—"
Sirius stole the quill and tucked it behind Severus’s ear, grinning. "Keep it. Souvenir."
Severus frowned. "Biologically redundant. We shed keratin daily."
Lily made a noise like a dying hippogriff.
Sirius leaned in, whispering something that made Severus’s ears turn pink. He nodded gravely. "An experiment worth replicating. Though your proposed angle lacks proper lumbar support."
Lily tackled a suit of armor. It clattered to the ground as she wailed into its visor.
Severus, meanwhile, was clinically observing Sirius's reaction to having his earlobe nibbled—documenting pulse fluctuations with one hand while pinning Sirius against a bookshelf with the other. "Interesting," he murmured against flushed skin. "Vasodilation increases markedly when—"
"Merlin's saggy left—" Lily hurled a dictionary at them.
Sirius moaned into Severus's mouth—a sound suspiciously close to 87 decibels. Severus's free hand twitched toward his pocket notebook.
"NO." Lily stomped on the notebook. "No. More. Metrics."
Severus blinked down at the crushed parchment. "You're impeding scientific progress."
"I'm impeding a homicide charge," Lily hissed, gesturing at Sirius—who was now arched against the shelves like a bowstring, fingers tangled in Severus's robes. "Look at him! He's a public indecency violation waiting to happen!"
Severus tilted Sirius's chin up with two fingers. "Respiratory rate: 42 breaths per minute. Pupillary dilation: 8 millimeters." He leaned closer. "Shall we test refractory periods?"
Sirius whimpered. Lily screamed into her robes.
Somewhere behind them, Madam Pince's screech echoed: "NO SEXUAL PHYSIOLOGY IN THE ALCHEMY SECTION!"
Severus straightened his collar. "Inaccurate. We're in Ancient Runes." He turned back to Sirius. "Now, regarding your earlier hypothesis about kneeling angles—"
Lily Apparated away. (Or would have, if they weren't in Hogwarts.)
Instead, as Remus walked in she dragged him over my his scarf. "Fix this."
Remus took one look at Sirius—now murmuring something about "experimental repetition" against Severus's throat—and sighed. "They're adorable."
"Adorable?" Lily's voice cracked. "He's got a flowchart in his back pocket!"
Severus adjusted his glasses. "Pie charts are more effective for comparative—"
Sirius kissed him quiet.
Remus nodded approvingly. "See? Cute."
Lily collapsed onto a pile of enchanted encyclopedias. They hissed at her. She didn't care.
Somewhere between Sirius's teeth on Severus's collarbone and Severus's hand sliding under Sirius's shirt ("Fascinating. Your sweat glands exhibit—") Lily lost the will to live. She grabbed Remus by the robes and hissed, "Do something or I'm setting the place on fire."
Remus eyed the scene—Sirius now straddling Severus's lap while Severus clinically measured his pupil dilation with a ruler—and grinned. "Aw, but they're adorable."
Severus looked up, ruler still hovering near Sirius's eye. "Adorable is a subjective descriptor lacking empirical—"
Sirius kissed him, biting his lower lip just enough to make Severus's fingers twitch against his waist.
Remus tossed a pillow at them. It bounced off Severus's head.
Sirius laughed, bright and unrepentant, tangling his fingers in Severus's hair. "He's cute when he's clinical."
Severus blinked. "Cuteness is evolutionarily irrelevant."
Remus laughed. "Mate, you're so screwed."
Severus tilted his head. "Anatomically impossible given current—"
Lily screamed into her hands. Sirius, meanwhile, looked downright delighted. "Wanna test that theory?"
Severus considered this. "Hypothetically, if we—"
"No!" Lily lunged across the table, clamping a hand over Severus's mouth. "No hypotheses! No testing! Just—" She gestured at Sirius, who was currently attempting to nibble Severus's earlobe while simultaneously undoing his top button. "Please. I swear I will give you my firstborn child if you make this stop. Just make him stop."
Severus blinked, then pried Lily's fingers off his face with clinical precision. "Your offer is illogical. Firstborn children statistically reduce productivity by—"
Sirius took advantage of Severus's momentary distraction to slide into his lap, knees bracketing Severus's thighs. "Oi, Evans, stop interrupting my boyfriend's very important research."
Severus frowned. "Boyfriend is a colloquialism lacking precision. Our relationship defies traditional labels given the—"
Lily made a noise like a teakettle exploding. "Did you just—labels—*boyfriend*—"
Sirius grinned, hooking his chin over Severus's shoulder. "He's adorable when he's flustered."
Severus stiffened. "I am not flustered. My physiological responses are well within—"
"Yeah?" Sirius traced the rapid pulse at Severus's throat. "Then why's your heart doing that?"
Severus grabbed Sirius's wrist, holding it away like contaminated evidence. "Statistical outlier."
Lily groaned, dragging her hands down her face. "I need firewhisky. And obliviation. And possibly a new set of eyes."
Remus, who had been watching the proceedings with quiet amusement, finally took pity on her. "Alright, Padfoot, stop terrorizing Lily. Severus, stop measuring Padfoot's saliva viscosity in public. Both of you—" He paused, glancing at Severus's lap where Sirius was now shamelessly grinding. "Merlin, never mind. Just... take it to your dormitory."
Severus adjusted his collar with academic severity. "Unnecessary. The library's acoustics provide superior—"
Lily tackled a pillow over her own face. "I can't believe this is my life."
Sirius, undeterred, nipped at Severus's jawline. "C'mon, science boy. Let's go replicate some findings." His fingers crept under Severus's shirt, eliciting a rare, sharp inhale.
Severus stood abruptly, dragging Sirius up by his belt loops. "Fine. But we're documenting everything."
Lily whimpered into Remus's shoulder. "Kill me."
Sirius grinned, letting Severus manhandle him toward the door. "Don't worry, Evans. I'll return him in one piece. Mostly."
Severus paused in the doorway, adjusting his glasses. "Unlikely. Given previous data, tissue integrity is compromised at approximately—"
Sirius kissed him silent mid-sentence. The door slammed shut behind them.
Lily stared at the ceiling. "I created a monster."
Remus patted her shoulder. "But a happy one."
The library door burst open again—Severus striding back in, rumpled and flushed, dragging a protesting Sirius by the collar. "Forgot my notebook."
Lily groaned as he snatched the *Fig. 5: Seminal Fluid Volume* parchment from the floor. Sirius waggled his eyebrows at her over Severus’s shoulder. "He’s very thorough."
Severus adjusted his askew glasses with one hand while clinically examining a fresh hickey on Sirius’s throat with the other. "Fascinating. The capillary rupture pattern suggests I bit harder than Trial 7—"
The door slammed shut. Lily’s scream rattled the chandeliers.
Remus sipped his tea. "Well. That happened."
Lily’s forehead hit the table with a thud. "I’m putting myself in Azkaban," she mumbled into the woodgrain. "Voluntarily. Tonight."