"Can you tell me at least one more time why I'm doing this," you say, still unsure as to how you've managed to find yourself in Twilight's potion room.
You can tell that you've said something irritable, but Twilight manages to maintain her professional demeanor. "This is an experiment to see which potion you choose over the others."
"Can I not?" you ask. You know fairly well that if Twilight and potions are involved, something weird is going to happen.
She seems to shrug, "I suppose that's an option. Considering this is more of a test of social knowledge and trust, I could put down that you are not sure of the outcomes that may occur and opted to not trust me in my assurance that nothing bad would happen to you."
That's harsh. You're no quitter! After all, this is Twilight we're talking about. She's not the kind to plan something devious behind your back or anypony elses! You take note of your choices, carefully arranged by color. Each one is kept back so you cannot smell any of the fumes that are coming from them, and even worse on your psyche is that each potion has a number attached to it that Twilight tells you that it removes after the liquid is gone, revealing what you just drank.
Green. That's a color that usually means poison, but that's what she wants you to think. She wants you to choose anything but green. She's even looking at it and then back to you in a worrying way, you have her!
You down the green liquid which was marked with a number '4' on it, only barely remarking on the taste of green apple as it goes down your throat posthaste. The number falls, your confident smirk tells Twilight that you've won before you look at what is on it. '63'
"The heck is a '63' potion?" You question before your gut decides to begin attempting backflips. Your body feels wrong and its now doing everything in its power to adjust accordingly. The strong chin you've been proud of? It's smoothing away, like somepony is gently rubbing it off. Those powerful legs that made you run for days on end and could knock over most anything? Make way for slender and flexible legs that would make other mares jealous.
Oh, and that bit involving your gender there? Now it's the reverse part.
The transformation finally over, you clonk a hoof on the table to right yourself again. You've become a little shorter in height and your balance is off due to that shift of weight and muscle that just happened. Your look of utter shock meets Twilight's happy expression as she giddily clops her hooves together.
"I had been hoping you chose that!" She squeeks. "In case you needed to know, Potion No. 63 is a gender reversal potion! I had been saving it for some time, and I'm glad that I finally got to see the effects before me!"
"Why d-!?" You start to yell before freezing, hearing your new voice as it sensually escapes your puffed up lips.
"Simply put?" Twilight started, before revealing her own green potion. "It's like I said. This is a social experiment, and both of us are going to enjoy it.
Your eyes go wide as she downs the green potion.