The pain is surging from your pelvis and flooding down your legs, through your ankles, into your feet, and all the way down to your toes. But you can't see anything when you're belly down in the dirt, so you roll your self over and push yourself into a seated position. Finally sitting on your butt you can look forward with some hesitancy at your feet.
"What the he-EEE HAAAWWWW!"
Your feet are stretching out, taking on a almost a tubular-like shape as they grow. Soon they look like they're almost as long as your legs! But something else is wrong, you're toes feel funny. Looking down, you see their skin is sticking together, almost like they're webbed. But it's more than the skin: the toes themselves are moving together, bone to bone, joint to joint, nail to nail. Looking over at Lyra, you see her wincing from the same cramps, and more importantly, you see all her toes have joined together into a single round, bony mass at the ends of her legs. Within seconds, your own have followed suit, until you can see and feel what seems like just one toe at the end of each leg.
The cramp moves into your cuticle, followed by a surge of pressure forcing something out through your toenail. It looks like your nails are growing larger, thicker, darker. Before long, your toenails have expanded to become huge round keratin toe-protectors that are unmistakable as hooves.
"Aw, fuck, it's happened again," says Lyra, reaching out toward her right hoof. You look down and twitch what looks like your angle. Your hock contracts, and what's become your new canon lifts, bringing your left hoof higher in front of your eyes. You try to wiggle your toes but only manage to wave your new donkey fetlock up and down.
Looking over you see Lyra holding on to a wall of the pen, trying to get her altered legs to take her weight. Knowing that you and she will be doomed if you just sit and wait for more changes, you start trying to stand up, too. It takes a while; these feet were clearly not meant for standing on just two feet. But you don't want to stick around and end up with four feet, so you do your best. After falling down multiple times, you finally get yourself into a wide stance, carefully balancing your torso over your numb equine hooves. After some further practice, you even manage to waddle forward in big, awkward steps.
Then you hear Lyra's voice again, saying, "Don't look at me," but of course that only draws your attention and your eyes are on her before you've understood fully processed her words and stopped yourself. She's up on her two hooves, leaning forward with both hands against the wall of your pen, and then a yellow liquid spills out from her groin to muddy up the earthen below. "There's, there's no toilet here, and I haven't gone since last night, and pl-HEEE-ease don't judge me."
At this point you wish you could respect her privacy and look away, but the smell is starting to reach you and has you mesmerized. You wobbled forward. Her flow trickles to a stop. You don't understand why you have to get closer. But you breathe in a long deep whiff of the air around this stall and suddenly the smell of FEMALE fills you to your core. You need more of that smell. You spread your nostrils and curl your upper lip. Something about the smell of FEMALE pouring in through both your nose and mouth tickles every cubic inch of your body, your mind, and even possibly your soul. Your penis, which had long since shrunken flaccid in your fearful state, rose tall and rigid like a solider ordered to attention.
"What are you doing?" asked Lyra, having witnessed your approach, your instinctive flehmen response, the dazed look on your face, and of course, your rapid erection. You try to snap yourself out of it.
"I, I, I, I---" you aren't sure what to say. Can you salvage the situation? Will she think your a disgusting? Will she still let you help her find a way out of here? Will the... will the FEMALE let you fuck her? While her pheromones are fresh and fertile?