> Be Anon, finally at that point in your relationship with Celestia where you can share intimate moments without feeling embarrassed
> Ppppffffffttt
> "Ugh, Anon, what did you eat?"
> You snuggle her long neck as she turns her head away
"Egg salad sandwiches, same as you. Smells like roses, right?"
> Celestia rolls her eyes
> "If they grew in volcanic soil, maybe. You're lucky you're cute."
> You kiss her on the cheek
"I sure am."
> She snorts, but doesn't pull away
> Her horn glows briefly, wafting the smell away, and she relaxes against you
> You relish her warmth, and the soft feel of her fur under your hand
> She stretches out across your lap, then relaxes
> Pffweeet
> You grin down at her
"You're lucky you're cute."
> She blushes
> But something about her retort strikes you as odd
"Where did that come from? Because it sure wasn't your royal rump."
> Celestia pouts
> "It could have been!"
> You shake your head
"I was watching. Not a jiggle. Not a slight cheek lift. Nothing."
> She buries her face into the couch cushion and mumbles something 
"What was that, sunbum?"
> She lifts her head and sighs
> "That was my hoofbutt."
> You grab her head and look her dead in the eyes
> She's clearly embarrassed, but you don't see the telltale twinkle that usually leads to ponies being traumatized via phoenixes
"What, exactly, is a hoofbutt?"
> She sits up and brings her hind leg onto your lap
> "See? Behind the straturn medium, the two soft cheeks?"
> You hold her hoof and rub your thumbs across the rounded fleshy part
> Sure enough, you can spread the two cheeks apart to reveal a puckered sphincter
"This makes no goddamned sense."
> She shrugs a wing
> "I thought it was weird that your feet don't have them, but you don't really have the foot structure to protect them, so they probably atrophied in your species's development."
> You pinch the bridge of your nose
"That... Look, we have horses back home, and they sure as hell do not have hoofbutts."
> Celestia looks at you dubiously
> You grab a sheet of paper and draw a circle, an open bottomed triangle with the point in the middle of the circle
"See, this is roughly the structure of a earth horse's hoof. The frog of the hoof is inside the triangle, then there's the sole of the hoof, and the straturn medium around that."
> She raises an eyebrow
> "Are you sure you're not remembering that wrong?"
> You feel like you are on an episode of the Twilight Zone
> You are pretty damn sure
> Like, 99% sure
> At least 98% sure
> You look around, and feel a wave of relief wash over you
"Yeah, I'm sure. See, if I draw some stick figures on either side worshipping the frog of the hoof, then it looks just like the stargate address for Earth."
> Celestia looks up at the giant stone ring portal device in your living room
> "Huh. So that's what that was."
> You nod
"Back when you guys came over the first time, you inspired the cult of the meemaroh nohuves, and that shaped the iconography you guys set for our world."
> Celestia nods, but she's been distracted as you've been playing with her hoofbutt
> She takes a shuddering breath
> "Anon, would you be open to a bit of experimentation?"
> You raise your eyebrow at her
"You want me to stick it in your hoofbutt?"
> She nods with an eager smile
> You look down at her hind leg
"Will it even fit?"
> She snorts
> "Anon, look it up on clophub.crys, there are plenty of examples of hoofbuttplay."
> You shake your head
"I swear, you guys really are made out of marshmallow."
> Celestia smirks
> "You're lucky Twilight didn't hear you say that, or else you'd have to endure her lecture on sucrose-based biochemistry again."
> You huff
"I still say that's bullshit how your species is entirely composed of diabetes."
> "Jealous?"
"Always. So, should I get some lube or what?"
> Celestia floats the dispenser into your lap
> "Use plenty, the hoofbutt isn't really meant for insertion."
---
> An hour later, the two of you are panting and shuddering in the afterglow
> You could get addicted to that tight little hole
"Wait, do you poop from there?"
> "No comment."