"...after 12 hours, both parties may switch back." You tried to grasp that slippery fact as the donkey now in your human form keeps talking.
It's just after noon. That means you have to remain in the body until midnight before you can even attempt to switch back. "That's good," you think to yourself. "It won't be fun, but I can tolerate this for 12 hours..."
But the new man keeps talking aloud.
"So after 12 hours, I suppose we could conceivably switch back," he says in your voice. "But there's a 12 hour time limit in doing so. Once that 12 hour time limit is over, both parties are stuck with their new bodies permanently, and the Zulo medallion will cease to affect either party from now on."
You feel a definite chill pass along your donkey spine. You realize you must swap back into your human body within 24 hours.. or perhaps more like 23 hours and 30 minutes, more or less.
You try to organize your thoughts. "You've got to keep that medallion safe..."
You blink your big, dull eyes. The man is walking away.
"Wait! Stop!" You hear your protests manifest as discordant brays. "Where are you going?"
He takes YOUR keys and gets into YOUR vehicle.
You bray wildly. "You can't leave me like this! Come back!"
The car blurs into a gray shape before it speeds out of sight.
"Oh fuck!" You bray loudly as you make the discovery that your donkey body doesn't move with undue haste or speed.
"Ok..." You try to breathe. HeeHuff HeeHufff... You inhale and exhale noisily, your wide nostrils at the end of your broad snout flaring.
"I have got to get home...make that donkey change us back!"
That plan soon meets a snag. The entire pasture seems to be enclosed by a fence. Why couldn't the medallion have switched you with a strong, muscular horse capable of leaping a tall fence. You can barely lift your heavy hooves off the ground. You'll never be able to jump the tall fence!
"I'm trapped!" You begin braying in real panic this time, trotting the length of the pasture, testing different areas of a very secure, very maintained fence. You feel your long black donkey cock slip from its sheath.
As your hooves clop on the ground and grass, you realize it's 10 miles to town and your home. Even if you escape the fence, how fast can you travel?
But you can't give up! You can't spend your entire life as a ugly, smelly, fucking donkey! You've got to find your former self and make him use the medallion to reverse this awful mess.