"Woah! Did you know that there's a tribe in Paraguay where facefucking strangers is still considered taboo?"

"Yeah, right..."

"I'm not kidding! Check this out: It says here this particular ethnic group retains a vestigial trait called a 'gag reflex' that's otherwise extinct in humans. Yuck, get this: Apparently this reflex can make people throw up when something touches the back of their throat. Eew, that's so nasty!!"

"Ooh, I think Professor Estell actually mentioned that once! According to him, most humans used to have that reflex, but it all but died out centuries ago. Nowadays its only found in extremely isolated populations. They consider it rude to throatfuck people without permission because you never know if they're gonna retch on your junk. Crazy, huh?"

"Dude. Imagine living like that. I think I'd kill myself if I had to retch every time someone stuck their junk too far down my throat."

"Yeah, thank God for evolution. I don't know what would be worse, not being allowed to just throatfuck whomever I liked or risking puke in my crotch whenever I did."

It struck me once again how lucky I was to have found Keira as a study partner. She had a real knack of making each tiny little detail come alive in your head and making you imagine it (even if sometimes that meant imagining girls puking on my cock). That way, the facts really stuck in your head because you had Keira's little stories to associate them with, and that made them that much easier to recall in exams. Her silly scenarios had saved my ass more than once when I was about to epically fail a test.

Right now, we were studying for our final oral exams in sexual anthropology. So far, it was going pretty well. We made sure to take regular breaks to give our brains some rest and blow off steam. We had just finished one such break -- from my seat on the couch, I could see my cum still slowly oozing out from between Keira's labia as she kneeled on the floor, organizing her materials and looking for the next topic to study. As I watched my seed slowly make its way down her inner thighs, I realized that I had been absentmindedly stroking my dick, which was already starting to turn hard again. Dammit! I had been doing so well not getting distracted outside of our breaks!

I cast my eyes around the room, trying to clear my head and get back into studying mode. Keira still lived with her parents, who were pretty much what you might call "filthy rich". Her bedroom was extravagantly decorated; she had a lavish four-poster bed with a canopy and the softest mattress I had ever seen, and her nightstand was brimming over with ridiculously expensive sex toys, all in immaculate condition despite their frequent use. Above her desk, she had hung a collage of pictures of her female friends, all in various states of undress, interspersed with the best dick pics she had gotten from her male friends. The wall across from her bed sported her most prized possession: A giant canvas treated with a special chemical that reacted when semen touched it, erupting in flurries of different colors. I remembered when she had painted it: She had gotten all of her male friends together and gave them precise instructions as to how and where to spill our seeds, fretting and fussing and nearly having a nervous breakdown when Callum had carelessly shaken off a few drops over an area where Jesse's cum was supposed to go. In the end though, everyone had agreed that she was a uniquely gifted cum artist, and you could still see the pride on her face whenever she looked at her painting.

None of this was helping me with my boner problem though, so I decided to do the pragmatic thing and just roll with it. I got up, slapped Keira on her right buttcheek, and suggested we test each other. "Good idea," she said, divided our flash cards into two stacks, handed me one, and lay down on the sofa, her head leaning against the armrest. I climbed up after her, straddled her so that her face was between my legs, and inserted my now fully erect cock into her waiting mouth. This way, neither of us could see the flash cards the other was holding, so there was no chance of either of us cheating.

We took turns asking and answering questions, and I was pleasantly surprised to realize how much of the subject matter I'd already been able to retain. Keira, on the other hand, was struggling slightly: It wasn't so much that she didn't know the answers, but rather that she was having trouble enunciating properly with my shaft sliding in and out of her mouth. The ability to speak clearly with a full mouth varied from girl to girl, and Keira had always had slight problems making herself understood while her mouth was preoccupied. This was fine during day-to-day conversation, but during an exam it could prove fatal.

"Keira, I'm sorry, you really need to work on your pronunciation. It's most likely going to be Estell testing you, and you know he won't go easy on you just because you're having trouble forming words around his monster cock. Slurping and gagging aren't the answers to everything, y'know?"

"Ell, ool agga ungngang err enkng oo!"

"Sorry, what was that? Try again," I smirked, thrusting my hips forward and forcing myself even further down Keira's struggling throat. She inhaled sharply, sucked tiny rivers of spit out of her mouth past my cock, and scrunched up her face in concentration.

"I said", she forced out, the words coming out clearer than ever before, "that you will have to understand their questions too, asshole. Gatehouse will be on the board as well, remember? So, unless you really want me to believe you won't jump across the examiners' table and drill her skull the moment your exam begins, you're gonna have to practice understanding gargled questions."

I had stopped thrusting after the first few words to gaze in astonishment at her convulsing throat and leaking mouth while she was forming complete, comprehensible sentences, and she took that opportunity to grab me by the hips and push me out of her. My boner slipped out of her throat with a wet PLOP, spraying saliva and precum all over Keira's laminated flash cards. She let go of my hips and reached for my cock, cradling it playfully between her cheek and her shoulder.

"I guess we both have to practice if we don't want all this revision to be wasted," she said glumly. "Well, at least I'm lucky I don't live in the dark ages and that a dick in my mouth only means I have to watch my words and doesn't make me fucking PUKE. I'm still not over that one. You know how sometimes babies get born with vestigial tails and shit? I wonder if like one in a tousand girls or something is still born with a gag reflex..."

"OMG, Keira, you actually believe that gag reflex myth??" A shrill voice had interrupted Keira's musings. Her bratty little sister, Mia, was standing in the door. She had just had her Cumming of Age ceremony last week at her posh boarding school and was home for the weekend. She had been free to use for less than a full week, but of course she thought she already knew everything there was to know about sex.

"Honestly, some people are so DUMB. Yesterday Emma told me her brother had told her women used to have no control over their pregnancies! Like, you'd get a creampie, and BOOM! Insta-pregnant! How could anyone believe that. I mean, just look at this," she gestured towards her legs. Her tight jeans were ripped and torn in several places, and her crotch was fully exposed. Her smooth, tight little teen pussy was drooling semen, and she had left an unmistakable trail of small, wet puddles when she had ascended the stairs to Keira's room.

"Look! This is at least seventeen guys, and that's just from the ride home today! How would you ever not be pregnant? How would you know the father? It's just ridiculous."

"I'm proud of you for taking such a keen interest in sexual anthropology, little sis," Keira said with that evil grin every older sibling got whenever they were about to exert their authority over their younger family members, "In fact, since you obviously put a lot of thought into myths about ancient people's sex lives, I bet you'd like to help us with a highly scientific experiment?"

Mia looked skeptically from Keira to me -- and suddenly dashed out of the room, sensing a trap. But Keira was quicker. She pursued her little sister to her own room and managed to force her way inside before Mia could lock the door. "Gotcha," she boasted. "Now. Kneel. Jon, c'mere!"

I got up, wiping Keira's spit off my dick using her favorite skirt, and followed the girls.

Mia's room was the most typical teenage girl room imaginable. Everything was a sickeningly sugarish pink -- the carpet, her bed, her wardrobe, her buttplugs -- and the walls were covered in posters of hunky movie stars presenting their perfectly proportioned, expertly groomed boners and dolled-up teen pop singers pouring martini glasses of cum over their photoshopped bodies.

Keira had forced Mia to her knees and was standing behind her, holding her down by the shoulders. "Now, my skanky little lab rat, you will have the honor of assisting my esteemed colleague Professor Jon Jackhammer with a cutting edge experiment. Open up!"

By then, I had guessed what Keira was planning, so I didn't bother waiting for my cue and simply started assaulting Mia as soon as she opened her mouth. I grabbed the back of her head with both hands and slammed her into my crotch. Her eyes bulged as my penis rammed the back of her throat and slid so far into her slender teenage neck that I was sure I would hit her rapidly beating heart any moment. The force of my thrust knocked the wind out of her and for a few seconds, she sagged slightly, so that the only thing keeping her from falling facedown on the floor was my erection holding up her skull. To her credit, she managed to gather herself quite quickly and grabbed a hold of my buttcheeks. But when she tried to move her head to pleasure me, Keira stopped her with a hand to the back of her head.

"Not so fast, girl genius. We are testing whether you have a vestigial gag reflex. Since you're basically still a virgin -- don't even try to complain, you can't have had more than a few hundred cocks in your first week -- chances are, if you were born with a gag reflex, you haven't had enough to training to get rid of it. So, you're going to keep the tool my colleague so generously provided lodged in your whore mouth until we're convinced -- or, if you're unlucky, until you throw up."

Mia glowered up at her mean older sister, but she didn't show any signs of retching. I renewed my efforts to impale her from above, reaching around her with both arms and pressing her into me as if I was trying to shove her head through my stomach. She was making little gurgling and choking noises, and she was having trouble breathing with her nose pressed into my belly, but there was no retching.

Keira was obviously disappointed. "Nice try, bitch. But don't think I'm convinced that you're not adopted." She gathered up a handfull of Mia's saliva that had collected around my balls and her chin and wiped it all over her little sister's face and into her hair. "You're gonna regret proving me wrong. Professor, I command you to make this fuckslut retch or so help me."

I looked down at Mia. She could barely open her eyes because Keira had glued them shut with her own saliva, and she was breathing heavily. I didn't want to go too hard on her, remembering how my own older sister had always whored me out to her female friends after I came of age, but on the other hand, she seemed to be taking it quite well. Also, she was still at the very beginning of her free use career and I would be doing her a courtesy by providing her with expert training.