"Well Pinkie, remind me why you want to do this again?" Twilight asked, shaking her head as she looked over her friend.

"Duh, silly." Pinkie explained.

"Well I'll do it, for science, and at the same time maybe we'll learn a little something about the each other." Twilight Sparkle said as she circled her friend, who was tied down to a steel chair with leather straps around all four of her legs and across her stomach.

Despite her current position, Pinkie wore a cheerful smile. "Ooh!" She squeaked, "I like learning new things about my friends!"

"Of course you do. Now excuse me while I read over this book again for a moment. We need to make sure absolutely everything is perfect before we begin." Twilight lifted her book and began to scan over the beginning. Theoretical Magical Conception for Eggheads

"Aha!" The purple unicorn slapped a page on the book before tossing it onto a small table. "Let's see here. It says that the vulva is the external opening of the reproductive tract. The labia are the lips of the vulva on each side of a five- to-six-inch vertical slit located below the anus. Something seems... wrong." Twilight looked her friend over once again, who simply shrugged.

"What's wrong?"

"Right, I see." Twilight trotted up to the chair and kicked a lever, which caused the steel chair to unhinge and the seat to fold upwards against the back. She then flipped it over so that Pinkie's plot was in the air and she was face down. "Perfect. Now your vulva is below your anus. It's all coming together."

"Woo! I'm accurate now!" Pinkie exclaimed.

"That you are, my cute little friend. Okay, now let's see." Twilight closely inspected Pinkie's exposed plot and genitalia. "Next is... the vagina. The vagina is comprised of a six- to eight-inch long muscular tube lined with mucous membranes. It connects the vulva to the cervix. The tissues of the vagina are very elastic so that it can accommodate the stallion’s penis, or unicorn's horn during breeding and magical insemination, and passage of the foal during the birthing process. Excellent, everything looks right so far. Your mucous membranes are clearly secreting, and we haven't even started yet. This is great!"

"That's because I'm excited, silly!" The pink party pony squeaked out in delight.

"I can tell!" Twilight returned her excitement with a bright smile. "Okay, now for the important part. When a mare is in estrus, she may be more irritable or less pleasant to be around. This fact is attributed to her urge to breed. When not breeding, a mare in estrus only has one thing on her mind, and everything else is considered to be a hindrance towards that goal. The estrus maximus, or extreme point of heat, only lasts a few days, while the full heat cycle can last for months. During estrus maximus, the signs are most noticeable."

"Am I irritable lately?" Pinkie asked.

"Not that I've noticed, but according to your cycle-calendar, today should be day two of your estrus maximus." Twilight tilted her head and poked into Pinkie's vagina with the tip of her hoof.

"Mmm! Juicy!" Pinkie shouted from her chair.

"It sure is. Okay, so let's go on then. Magical insemination: While little has been scientifically documented about this rare phenomenon, it is widely known that unprotected horn-sex can lead to an unwanted pregnancy. Hehe, well this one isn't exactly unwanted, now is it?" Twilight leaned in front of her friend and winked.

Pinkie returned the wink with a drawn out giggle.

"Through private trials and clinical testing towards development of a new form of birth control, some information has been recorded. It's said that the mare needs to be in estrus maximus in order conceive magically. This is because when a mare is in estrus maximus, the cervix is flaccid and fully opened to facilitate the passage of magical residue and all agents that may reside within that magic. You seem to be in EM to me, I just don't know for sure." Twilight placed a hoof to her chin, then leaned in to sniff her friend.

"One way to find out." Pinkie said as Twilight took a deep whiff.

"You smell like you're in EM... but you're right. We won't know til we try. There's more to read as well. Secondly, in order for the mare to conceive magically, it has been noted that she needs to be in a state of full ecstasy and mid-orgasm during the horn-spurt. Due to the varying nature of the activities required to achieve these two events simultaneously, it's difficult or impossible to plan the timing. Okay Pinkie, are you ready for this? I'm about to put my horn inside of you and move it around. Make sure to tell me what you like so that I can get you in a state of full ecstasy, okay?"

"Okay. I will." Pinkie cheerfully replied while wiggling her tail beneath Twilight's chin.

The purple unicorn closed her eyes and gulped, then leaned down. She gasped and bit her lip as she felt the heat radiating off her friend's plot and enveloping her horn. With a lick of her lips, she pressed forward, prodding against Pinkie's hot, moist lips.

"Wait!" Pinkie shouted. "I'm not ready yet!"

"What? Why? What's wrong?" Twilight quickly backed away and trotted around to face her friend.

"Sheesh Twi, you can't just go shoving it in. I'm hardly even aroused at all yet." Pinkie explained.

"Oh... well uh... right." Twilight blushed and backed away. "So what should I do?"

"I dunno, turn me on."

"Ooookay..." Twilight glanced back over her shoulder, spotting a book that might be of use.

Sexual Excitement: A Beginner's Guide, She grabbed it in her aura and began to skim.

The physical stimulation of an erogenous zone or acts of foreplay can result in arousal, especially if it is accompanied with the anticipation of imminent sexual activity...arousal may be assisted by a romantic setting, music or other soothing situation... The potential stimuli for sexual arousal vary from pony to pony, and from one time to another, as does the level of arousal... note clitoral blood levels fluctuating... labia stimulation and temperature shifts...

"Gah! This is all so complicated!" Twilight threw the book over her shoulder and trotted back up to Pinkie. "Hmm, I'll be right back."

"Um... Okay." Pinkie frowned and hung her head while she waited, still suspended face-down in the bottomless chair.

Twilight soon returned with a variety of items floating in her aura. "Here we are, this should make things go a little more smoothly." The mare lined the desk in front of Pinkie with several candles and turned on a record-player, which began playing slow-paced, deep base along with a low-voiced stallion singing.

"Romance, check. Music, check. Soothing setting? Um, check." Twilight began massaging Pinkie's sides and flank as she relifted the book and skimmed.

Right, clitoral blood levels and labia stimulation.

She looked Pinkie's vagina over and measured up the level of apparent sexual arousal. She poked at a small nub at the top and noted her friend's reaction. She then pulled on the labia and stretched them down with her magic, inspecting them and the inside as thoroughly as possible. "Are you enjoying this?" She asked with a raised eyebrow.

"I'd be enjoying it a lot more if you'd lick somethingI" Pinkie shouted.

"Hehe, irritability, check!" Twilight giggled. "Okay, lick something... here goes."

Pinkie closed her eyes and shuddered while Twilight's hot breath washed over her exposed plot. The unicorn brushed the bangs out of her face, then stuck her tongue out and delivered a lick from the nub all the way up to the base of her tail. She noticed Pinkie struggle against her restraints, and the squeak that accompanied her action. Twilight smiled and wiped her mouth, then went back for another taste.

"Ah! I'm enjoying it now!" Pinkie screamed as Twilight's tongue stroked up the center of her plot.

"Oh! Great! Should I further stimulate your labia?" The unicorn asked, taking one in her teeth and pulling on it.

"Uh-huh" Pinkie muttered.

The unicorn widened her bite, taking as much flesh as she could in her teeth and forcefully sucking it into her mouth. She pulled back as far as she could, then let everything slip out, a string of jizz and saliva trailing from her mouth to Pinkie's crotch. She went back for more, her muzzle slipping between the soaked lips as her tongue penetrated. Pinkie's moans urged Twilight to push deeper, and she did as she swashed her tongue around the inside.

The unicorn then stepped back, her face covered in Pinkie's jizz, wet and slimy. "You ready yet?"

"Mhm..." Pinkie nodded.

"Great! I am too." Twilight closed her eyes and rubbed her hooves together, then plunged her horn into Pinkie.

The pink mare screamed out in ecstasy as Twilight swirled her horn around and around. The unicorn couldn't resist lowering a hoof between her own legs as her horn sparked and spurted with intense pleasure. She pulled out, then thrust it back in as hard as she could, and repeated the motion. Pinkie gasped and squeaked with each penetration, her body trembling and every inch of her aching for an orgasm from the tip of her nose to her hooves. The unicorn didn't let up, she placed her front hooves on Pinkie's flank and pulled her back against her horn as tightly as she could.

Twilight's body began to shake as well. Her tongue flopped out and her eyes rolled back as she felt Pinkie squeeze her horn. She pushed it in as deep as she could, quivering as her horn spurted an abundance of magical residue into her friend. Twilight then slowly pulled out, stumbling backwards as she wiped away the gooey slime dripping down her face.

"Think it worked?" Twilight asked, panting for breath.

"I sure hope so." Pinkie said, sounding equally as exhausted.

"Let me get you out of that chair, then let's go take a nap. I'm beat." Twilight used her magic to unbuckle the straps, allowing Pinkie to fall to her hooves.

"Okay, I could use a nice little nap after that." Pinkie trotted up to Twilight and placed a hoof on her cheek. "And Twilight... Thanks for helping me..." She kissed her cheek, then trotted away, blushing.

Twilight giggled and snorted as she followed after her. "No problem Pinkie... It was my pleasure."