"So, what exactly is this test for, Twilight?"

"Well, it's a test to determine a taste and texture comparison for various reproductive fluids based on viscosity and appeal, as well as nutritional value. Additionally, excess samples may be collected to test the viability of cross-species breeding genetics."

Twilight Sparkle sounds rather cheerful as she explains to the human, but her cheeks are lit up with a blush. She's actually hiding a bit of her intent in that poor attempt at techno-babble, but her smile is bright and wide as she looks up at her subject known as Chris.

"Thank you for helping me."

"... I have no idea what you're talking about. Couldn't you have gotten Spike to help you get whatever... fluids you need?"

"Oh, this is a specific study about how the substances in question react with Pony physiology. Dragons have already been studied, but a human...!"

Twilight giggles excitedly and clops her hooves together. A human is completely new to modern science in this fashion!

"You seem pretty excited, heh... Well, okay. What do you need me to do, exactly?"

Chris sits up from his chair and walks up to the giddy pony, looking down at her curiously as her eyes remain focused somewhere lower than his face.

"Well, first, I'm going to need you to strip down so I can take notes on your physiology properly."

Twilight’s magic levitates over a notepad and quill as she smiles at him, eyes flicking from his crotch and up to his face, trying to look innocent, all the while her left ear is twitching irregularly...

"Okay, no harm there."

The human carefully pulls his shirt off and lifts it gently from his chest, letting it briefly hang from his arm before he drops it to his side. Unbuttoning and unzipping his pants before inching them down to his ankles, Chris tries to get this awkward moment over with so he doesn’t have to be a specimen under Twilight’s study for too long.

After he kicks his trousers away, he hears a sound similar to Twilight licking her lips as he is left in only his boxers. When he looks over to gaze at the mare, however, she seems to instantly look away, as if embarrassed. Chris raises an eyebrow curiously, but pays it no mind as he pulls his briefs down. In doing so, he reveals his soft member to the unicorn and leaving him completely nude, standing in the middle of the library.

"How's this?"

"Y-you don't have a sheath...?"

It's a questioning sort of observation, Twilight's quill scratching on the pad as she looks at the anatomy in question before she starts letting her eyes studiously roam his form. Chris responds casually, refraining from letting a blush appear on his face as he answers her.

"Err, no, I don't really need it."

"Ah, I'm sorry. That's exactly what I needed, thank you. Now, just stand still..."

The chiming sound of magic reaches his ears as she takes notes on the shape of his body. At least, so it seems, as her eyes linger on his form. Chris can feel her gaze boring into him as her magic starts to flit over his form, tracing his extremities and torso with purple rings of light and sparkles. He then feels an odd tugging sort of pressure, like a hand with no fingers, pulling along his flaccid shaft.

"S-sorry if this feels uncomfortable at all..."

"It's fine, go ahead."

As Twilight's tracing magic seems to analyze him from head to toe, the human feels a warm sensation, almost tickling him as it passes along. It follows her gaze to the letter, until it suddenly freezes on his waist. Slowly, it drags its way along his shaft, lifting it lightly like a palm would and tugs it gently. She quickly remarks that she is simply analyzing him, and he tries to push aside the growing concern that she might be doing more than that.

"It's fine. You can do... whatever it is you need to... It feels kind of nice, actually."

Twilight nods, horn aglow as she continues to caress his shaft with her magic, trying to see the factor of expansion it will display when he is aroused... but the scent of him is starting to distract her. She lets her magic flow off of him as she trots closer, inhaling deeply as if steadying herself.

"Would you... stand up and face away from me for a moment? I need to scan your back-facing profile as well..."

"R- right, of course."

Chris turns away after witnessing the pony oddly sniff the air, as if his musk is easy to sense for the mare. Facing the wall of books behind him, he hears Twilight take another step forward and decides to ask a question to dispel his worries.

"Are you okay back there, Twilight?"

"Oh, yes, perfectly fine! Why do you ask? Do I seem like I'm not?"

Her tone sounds a little panicked, the answer coming out very quick. Once he's facing away, however, she takes another scan of his body from behind, eyes locking on his musculature and admiring his rump as her tail flicks outward. It is quite a nice view, at least for her, and as she licks her lips, she imagines what she wants to do when she has him turn around again.

This starts to make Chris feel a little uncomfortable, but he can't help but feel a bit warm as Twilight runs her magical trace along his back as well. In fact, the sensation even seems to arouse him slightly, as he feels blood flowing to his member, bringing about a small twitch as it responds. Once the magic reaches his feet, the human turns to look back at her, but realizes he doesn't quite have the motion of his head to see her directly behind him.

"Do you need anything else, Twi?"

"A-ah, yes, uhm, turn back around and face me, please."

Chris notices her glance away from him for a moment before she resumes her analyzing. Twilight swallows nervously, eyes flicking over his form again as her magic pulses over his body as he moves. The majority of sensation from the unicorn’s magic seems to dwell on his reproductive parts; a rolling gentle wave of encouraging pressure moving along his shaft combined with a tingling over the surface of his scrotum as she tries not to look at his genitals so blatantly.

"A-at this point, we should collect the sample fluids..."

For a moment, he doesn't know what to say, and quickly lets out an excuse, hoping that she didn't mean what he thinks she means...

"S- So you want me to, like... shoot off... in a cup, or something?"

The human still doesn't understand why she licked her lips earlier, but he holds out hope it didn't have to do with the task at hand.

"W-well, you could do that, or into any container... "

She inhales deeply to brace herself, tail swishing from side to side as she sits in front of him, easily on the level required to assist him with that particular task, if he so wished. She looks up at him nervously before adding her simple, yet utterly blatant, explanation for her actions.

"I... I think I need a few results of it from you... ah... fresh."

That word, fresh, seems to ingrain itself in the human’s head as he takes a brief step forward and allows a nervous gulp to escape his throat. With the unicorn with sparkling eyes and her tail swishing very happily about this outcome, Chris can't help but feel a sort of... need emanate from her.

"What exactly... are you going to do?"

"I-... I think I need to sample it... directly... for texture and..."

She pauses to gulp loudly, eyes looking pointedly at his shaft as her magic attempts to make him reach proper arousal.

"... flavor. I... I would also need to ingest a fair portion of it in order to judge its nutritional value as well as, ah... any other properties, for the sake of science and alchemy... to personally experience its effect on pony physiology."

At that point, Chris finally understands as it seems his body reacts a step ahead of him. With an emphatic effect, his hardness brings itself to full mast as he feels the magic constantly spreading its warmth all over him while his shaft pulses rhythmically.

"You want to... taste it?"

As the human speaks, still stammering all the while, he notices Twilight's mouth open slightly and her tongue makes it seem as if she's drooling.

(“She... she really wants this, doesn't she?”)

"A- And you say you're going to swallow it?"

For some reason, the mental image of Twilight sucking him flashes before his eyes and his manhood delivers a strong twitch that he’s sure Twilight's magic can allow her to sense. Finally taking another step forward, he displays himself only a few inches away from the purple unicorn.

"Y-yes... I would need to, aahh... take you in my mouth... and... taste your semen..."

She flushes as she licks her lips again, swallowing as if parched as her eyes seem entranced by the hardening shaft before her, front hooves shifting against the ground as her tail flicks yet again.

"...and... swallow it... almost all of it, in fact..."

Her cheeks are colored darkly as she thinks about it, mouth remaining open as she takes a deep breath. Her tongue hangs out slightly as she tries not to drool, but she's slowly being driven mad by the appearance and scent of his exposed sex organs in front of her face.

"That's not a problem... right...? M-me, uhm... s-stimulating you to orgasm... i-in my mouth?"

"I- I guess it couldn't hurt. Science is what it is, after all..."

He agrees nervously, but in reality he’s incredibly aroused by her embarrassed desire showing through her words. If he’s ready and she wants it, who is he to deny her the right to... experiment, he supposed. Chris reaches his hand forward and gently brushes his fingers through her mane.
"Just... don't use your teeth, hehe."

"Y-yeah... okay. Right. No teeth... so..."

She looks up at him, then back down at his shaft as her magic works over his length, before opening her mouth wide, extending her tongue and taking a careful lick across the surface of his hardened male organ.

"A-aahh..."

Holding her there in front of him, with her mouth wide open and her tongue sneaking out to get just a careful lick, is already too much for Chris. He might just give her a fresh sample right here and now if he can’t help himself. The human steels his body and brings her head closer until the underside gently rests on her smooth, salivating tongue.

“Ah- Your-...Your tongue-...”

Twilight tastes him as he sets himself on her extended tongue, and for the first time, seems to rather enjoy the "filthy" act of having someone's genitals about to enter her mouth. She's trying, though, to remain professional as her tongue starts to work over the underside of his shaft, dragging her saliva-soaked tongue along it as she tries to evaluate the flavor of his aroused member. Her breath, hot and humid, washes over his tip freely as she allows him to manipulate her head in order to achieve their combined goal: his orgasm.

As soon as she takes him into her mouth and wraps her lips around his shaft, he knows he’s not getting out of this one without giving her just what she wants. Her tongue is amazing by itself, but Chris can feel her every breath on his tip, every second getting more and more eager to taste him. He may end up climaxing sooner than he thinks if she keeps this up.

"That feels really... nngh... nice, Twilight."

Twilight flushes as she's praised for such a lewd act, her soft lips toying with his shaft as her tongue moves to work over the head, pushing back the skin that covers it so as to fully capture the flavor of him. If nothing else, she is thorough and methodical... but she's also apparently becoming more and more enraptured with his tool as she closes her eyes, ears flattening to the sides as she suckles on him gently. She lets him move her head as he wishes, but as he keeps his shaft in her mouth, she's starting to rather enjoy his flavor; it's very different from what she's heard about the taste of stallions from her more sexually active associates, but she seems to like it just fine as her effort fills the library with the erotic slurps of her work.

"T- Twilight..."

The mare suckles him as her face shows a look similar to that of adoration. This unicorn is enjoying every second of his member in her warm, moist, loving mouth, and now he’s getting quite close to finishing inside. This one thought seemed to turn over in his head as he considered his actions.

(“She's a pony, but she's just so good. Is this really even for the sake of science any more?”)

Once she stops and closes her eyes to lick all over Chris’ well-tended to flesh, he uses his fingers to grasp the back of her head and hold her steady as his hips slowly thrust forward. The human isn’t quite sure how she reacts to his hips acting on their own like this, but he just can’t seem to help himself. He needs more of this amazing mouth of Twilight’s, and fast.

Twilight hums around him in approval of his taste as he grasps her head in preparation, the vibration of it running from her tongue and along his shaft as she tenderly suckles on him. Her lascivious new hobby, though, is interrupted, or rather, enhanced when he grips her skull and starts to thrust. She immediately connects the motion with the idea of a stallion trying to rut his mare... but... he's rutting her face!

Despite the realization, though, it only serves to arouse the lavender mare further, her eyes opening to look up at him as she finds her subject using her mouth as his personal pleasure-toy. All in all, she finds she rather likes the look and feel of him doing this, and so she decides to encourage even more of the behavior, locking her gaze on his with a lidded look of pleasure. She reaches up with both hooves to grasp at his hips as he thrusts, tugging him deeper as he helps himself to more of her mouth.

(“I really shouldn't be enjoying this, right? But... he tastes... good, and... and it feels so nice to have him thrusting into me, even like this... Oh, Celestia, he must think I'm such a whorse for this, but... I want more... maybe I can use my magic to help?”)

Her thoughts follow in this vein, somewhat distracted by the flavor and feel of him as he thrusts into her willing mouth, her horn starting to glow as she prepares a spell to assist their task...
Twilight seems to love the human’s treatment of her face, and he even starts panting as he tries to keep up with her mouth sucking him inward and his own thrusts into her. That's when he starts to notice her horn glowing a peculiar pinkish color.

(“Is she going to use magic? Now?”)

"Twilight, wh- what are you-..."

Indeed she is, but she isn't taking him out of her mouth if she doesn't have to and since she has decided that she doesn't have to explain when she could just show him instead, she just keeps at her work, starting to care less and less about appearing professional as she enjoys the simple, if filthy pleasure of his penis being thrust into her suckling mouth.

Her horn sparks before he feels the magic surge into his genitals and soak into them, a tingling sensation following along the paths of his body's workings until it reaches his scrotum... which starts to feel heavier as her magic works to increase the size of his coming release. It seems Twilight wasn't kidding about wanting a large sample size. With the effort she’s putting in, the mare must want enough for it to serve as a full meal, at this rate!

"Gah! Tw- Twilight!"

Chris feels the overwhelming tingling sensation of her magic worm its way through his member and into his scrotum. Immediately, it tightens before he starts to feel as if it’s getting... heavier!? This mare's obsessed with getting to taste human cum, and he is just about ready to succumb to her efforts. With a low howl, the human’s voice echoes through the library.

"Here you go, Twilight! Your precious... semen!"

His hands grip her head and pull her lips all the way to the base. The human’s member twitches violently in her mouth as it spurts out the hot, sticky mess all over her tongue and the roof of her mouth, with some of it going right down her throat.

Right now, Twilight is firmly occupied with trying not to choke on him as he hilts himself into her face. As he announces his release, though, her expression turns happy, as if she's smiling around his cock as it's buried in her mouth. However, when he starts to spurt, her eyes widen at the gushing amount as her tongue starts working diligently to stimulate his release to go for as long as possible.

She feels almost drunk with pleasure as she nuzzles into his crotch, inhaling his scent as he releases so generously into her mouth. The mare swallows as much as she can of each spurt, throat working quickly to take it all down, but she seems to, after just halfway through, have a perpetual mouthful of his jism to deal with. Her tongue, even still, slathers his member with attention as she savors his release.

To her surprise and simultaneous delight, he actually tastes rather appealing to her senses. Filthy images of getting him to season her food in the future flit through her mind, even as she considers asking him to allow her to do this for him again, quite soon in fact. She flushes darkly as she stores those dirty little ideas away, shocked with herself as to the extent her sordid little fantasies go.

"H- Haaaah...H- How was that...Twilight?"

As the final evidence of the human’s release is sucked into her mouth and she continues to baste him in saliva, Chris can only pant in response to the unicorn's eagerness. She definitely got her sample, that's for sure. Not knowing what to expect next, he watches Twilight and brushes his fingers through her mane before releasing her.

Twilight pulls off of his member with a disappointed sounding “hmph,” looking up to him and opening her mouth to pant for breath. In her mouth, coating her tongue and swishing around still, is a bit of his release. She pauses to swallow nervously after catching her breath, licking her lips as if to be sure she got it all down. Her eyes flick from his face to his member and she bites her lip before speaking.

"Th-that... was valuable test data... Next sample... will have to be collected properly for... intense study..."

Chris’ manhood twitches yet again as he sees her swallow every last drop and lick her lips of the aftermath. Twilight seems to have enjoyed that a lot more than her semi-professional attitude would let on. Upon hearing her say that she needs more than one sample, though, Chris quickly questions her.

"Pr- Properly? What are you going to do, Twilight?"

Twilight looks up at him and smiles sweetly. It seems a total disconnect from what follows...

"What am I going to do? Why, I'm going to suck your tasty penis again until you orgasm, and then I'm going to collect all of your semen in a beaker for proper study and analysis of composition and potential applications!"

Her smile catches Chris off-guard, but then her words throw him for a total loop. He chuckles nervously, not having enough room to back away from her.

"Ehehe, and...how many times do you need me to...you know...for you to have enough for 'analysis?'"

Chris starts to worry even more about her mentioning "potential applications."

(“Is this mare planning to use me like a semen dispenser?”)

Twilight continues to smile, leaning in to nuzzle at him with that innocent look of happiness still on her face.

"I would require at least four more samples, but I'm hoping for much more, if you're willing to cooperate! For science, of course..."

Her eyes shift to the side as she mentions science. It's more than likely she doesn't mean science at all, past the incidental discoveries at this point... but she's still trying to remain professional enough as to retain a proper sample for serious study and still have her fun.

Her nuzzling causes an immediate reaction as Chris’ member throbs, eager to feel her lips wrapping around it once more. The unicorn announced to him that she intends to get as many samples as possible, and with his mind addled by the previous orgasm, he can't help but nod slightly, agreeing with the mare's (under any circumstances, very unreasonable) excuse.

"F- For science...of course."

"I'm glad that you agree! Oooh... you're getting hard again... will you be able to give me another sample already?"

Twilight giggles before opening her mouth and taking a laboriously slow lick along him, her breath hot as it washes over him. Her tail flicks from side to side, before she settles into a laying position, legs tucked under her. Her mouth opens up for him, tongue extending as if offering him the chance to feed her a tasty treat.

"Aaahh~"

"Y- Yeah. Another... sample..."

The human gulps nervously, knowing exactly what he’s subjecting himself to as his lower half inches toward her and he rests his manhood on her long, eager tongue. Her eyes narrow and seem to become bedroom eyes as he hears yet another giggle escape her.

"I- I'm just giving you a sample..."

Her horn flares briefly as he's nudged forward from behind, pushing him into her mouth as she fixes that yearning gaze upon him. Having been taught by the princess, she was told that this look would make any male who knew the beauty of a mare weak in the knees. She's glad to see that it crosses species barriers so easily, as she begins to suckle softly on his hardening member.

"Mmmm-hmm?"

Chris winces, following the jolt of pleasure, before looking down at Twilight and seeing her gaze filled with a sort of knowing excitement. As she begins to suckle him, however, the human feels his need to question her being replaced by a need to go along with her and that smoldering look of hers. She looks... so beautiful... so desirable...

"Aahh...Twilight, your mouth feels...aaahh~"

His voice weakens as his body starts to feel very sensitive and vulnerable to the pony currently tending to his arousal. Chris’ hand reaches for her head to hold her steady, keeping his fingers along her neck to encourage her.

Twilight slowly swirls her tongue around him, dragging her tongue methodically over his every inch as she allows him to take her mouth. Suckling upon him gently and almost casually, her eyes drift shut. For her partner in this experiment, and anyone who might view the scene, it might seem like she's simply content to suck and nurse upon the human in her mouth now. His hand on her neck, encouraging her makes her moan quietly in pleasure around him, her head bobbing slowly unless he decides to move his hips on his own.

(“Oh goodness, she looks so blissful like that...”)

Chris can't help but nudge her along while his hips move in unison with her head, as it bobs gently up and down along his shaft. His words come without thinking, expressing the human’s true desire, even though he doesn’t immediately realize it.

"Th- That's it, Twilight~ Suck me..for your sample..."

(“She's gotten so good at this already, I don't think I can hold back if it means I get to feed- I mean... aid her research.”)

As she hums pleasantly over him, her suction begins to pick up force whenever he pulls back away from her face. Impaled upon his length as she is, she doesn't move her body even an inch, aside from allowing her tail to rise as she continues. Her neck and head are the only parts of her to move, bobbing herself upon him as lewd sounds of wet suction start to be heard through the library.

(“This-...This can't be happening, right? Semen's not supposed to be cultivated like this and yet she's sucking me with the full intention of letting her mouth take care of every last drop. With the way she's doing it, it almost seems like she's addicted to me, sliding her lips along my length with a brainless look on her face. It's too much, I- I have to...”)
"I- I'm about to...give you a second helping, Twilight~"

(“What was that? My voice is betraying me? My body actually likes having this pony sucking me with such eagerness?... I'm going to end up giving her a lot more, aren't I?”)

Twilight moans in anticipation, her horn flaring as a rather large glass container floats to their position, setting itself down beside Twilight's body. She then proceeds to suck on him stronger, her wet sounds becoming louder. In the air, he can detect a faint smell of feminine musk starting to get stronger... She’s quite noticeably getting aroused just by sucking on him like this, as she thinks to herself.

(“He's going to cum again~! That's fantastic! I wonder if it'll be just as much as the last time... Oh, or maybe even more! That would be great, I can get a sample and taste him again!”)

"It's a big sample, Twilight! Aaaaahhh~"

The human groans as the first spurt fires into her warm, wet mouth, immediately landing on her tongue and imbuing her with the taste she seems to enjoy. The shots just keep coming (no pun intended), as he gradually fills her mouth to the brim with the still ridiculous amount he has stored away, and when she can't seem to swallow fast enough, he sees the glass container she brought start to magically levitate closer to her face.

The glass moves up to Twilight's mouth as she pops off of him, her mouth opening as she inhales sharply through her nose. Her magic grips his shaft, buffeting it in a pulsing field of pressure to keep his release going. A few spurts of his release splatter onto her face, causing her to gasp at the warmth of it as it soaks into her fur, a strand of the semen soaking into her horn and making her moan like a raunchy comfort whorse. Still, her magic turns his spurting member to point into the glass, and continues to milk him into it for every drop she can manage.

Chris huffs as he tries to keep up with his body's expulsion of the powerful orgasm Twilight brought him to. When she takes the human out of her mouth, he notices the thick substance stain her face and horn before his member is unceremoniously tipped towards the glass container. She still doesn't let up, however, as he feels her magic drag the rest of the contents out slowly. As if he were a tube of toothpaste, the final few spurts are milked out of him and only a last drop remains on the tip. Chris watches her with half-lidded eyes for a reaction to the amount he gets into the container, even after filling her mouth so well.

"How...is it...Twilight?"

"It's so good..."

Twilight's hot, breathlessly moaned commentary is punctuated by a blush as she realizes what she sounded like, but right now, she's not too inclined to care about what she says. As filthy as the concept is, his sexual release has turned her on immensely. Especially because she achieved it using her mouth not once, but twice. Having had a thorough tasting of him and some of that seed from the last release still coating her tongue, Twilight answers in a dazed voice.

"It's a very... very good sample size... And... mmn~... you taste very... very good to me..."

He takes a brief step back from the mare, in an attempt to give her some space to breathe but the only thing she's breathing in is his scent and her own arousal wafting in the air. His cum is only turning her on more and more; she won't be satisfied with just two loads. Twilight really likes the taste of it, and this revelation causes Chris to stammer as he tries to respond.

"Th- That's all well and good, Twilight, b- but I- whoah!"

Chris takes another step back as he speaks and ends up tripping on a book she had accidentally left on the floor. Falling on his back, he groans in slight pain before realizing the position he’s in. The mare is looking unabashedly at his erection, still at full mast and with a bead of precum glistening under the light above them, as she licks her lips hungrily. Behind her, he spots her raised tail swishing giddily, showing her eagerness at whatever's going on in her mind at this very moment. Considering how vulnerable he is, the human believes he knows exactly where this is going...

Twilight slowly moves to stand, clearing her mouth of his semen and fixing a smile upon the fallen human. She trots over to him slowly and deliberately, almost like a predator cornering her prey as she licks her lips. Her tail flicks from one side to the other, fanning her aroused scent into the air as she comes closer. She reaches out with one hoof to press on his hip, keeping him down, as she leans down to carefully lick the bead of precum off of his member.

"Now that I have the samples I need..." she begins, her magic flaring and moving the collected sample in the beaker off to a safe place.

“Perhaps you can... sate my curiosity?"

With nowhere to go and with her hoof pressing into his hip, he knows the only outcome is the inevitable one. He is going to end up feeding this pony and probably even servicing that unyielding arousal of hers.

"I-... I'd be glad to."

The human’s hand reaches up to her face and she briefly nuzzles it, letting out a slight giggle before her eyes flick back to the object of her desires. Noticing the book to his side, Chris finds that he can just barely make out the title on the cover.

"Human Semen: A Pony's Guide on What to Expect From Your Unconventional Lover."

Somehow, he’s not surprised.

Author's Note

??? - Twilight
Exo - Chris

Exo: We’re doin’ science!
???: I think we can learn to put species differences aside. For science. You pervert.