Nothing seems to happen at first, so for a number of seconds you are breathlessly hopeful that this strange religion of theirs is just a self-congratulating superstition and that they can't actually turn you into whatever it is they are. That hope starts to weaken and fade out a little when the animals behind you start to "ooh" and "aah" and point out that "It's starting!"
You don't know what they're going on about at first, but you do notice that something feels disturbingly out-of-place at the very tip of your spine, at the very bottom of your back. You feel the oddest sense of swelling and even the occasional twitch as something starts to grow.
At first you manage to convince yourself that it's really nothing, since nothing's changed that you can see, and you certainly aren't turning your head to find out. These zoo animal people might just be crazy, since they aren't really human, after all. You just quietly cross your fingers, tune everything out, try to ignore the strange feelings from your backside, and focus on the fact that you still look perfectly human from your current vantage point, as far as you can tell. Unfortunately the thing you can't see doesn't stay hidden for long. While your gazing over the front of your body, priding yourself on how perfectly unchanged it is, something dark and hairy starts to appear from behind you, down between your legs where you can finally see it. But in fairness, you can't really see where it's coming from or what (if anything) it's attached to. A perfectly human kidnapping victim like yourself wouldn't have to worry about such a thing, right?
As the thick, furry object continues to lengthen below your knees, it continues to flex around a bit every so often, and it's getting harder not to admit that you can feel it moving. When it finally reaches the ground and you feel it make contact, whatever vestige of denial you had left is ripped away; you gulp and look again with pleading eyes at the elephant. He mutters something about the inevitability of life and the destiny of the soul, but you can't really focus. You have a new animal life to get ready for. You bend all the way over and stare between your legs at the long, thick tail that's swaying there behind them. It amazes you that you can feel it dangling there and make it move however you want. You reach between your legs and grab it, feeling the distant impact of your hands against it. You stand up straight again, holding your tail close in front of you to get a better look. The level of fine-grained control you have over it is really surprising. You can even wrap it around your arm like a tentacle. Had some higher authority really destined you to become an animal all along?
"It seems that the powers from beyond have chosen that you remain a prime," said the elephant. "A marvelous and rather unusual choice."
You're still getting introduced to your new tail when a spasm overtakes your feet. Your eyes widen when you feel your toes starting to twist and spread against your will. You let go of the tail and raise it behind you so you don't sit on it, and plop yourself down on your bottom with your legs spread in front of you. This way, you can watch whatever's going on in your toes without toppling over by accident. Something's definitely going on: your feet look shorter, and your toes are definitely longer. You flex them a bit on purpose, impressed by how easy it is for you to bend and curl them separately. A hard downward tug on your big toes, however, takes you by surprise. The base of each big toe shifting down along your feet, almost toward your ankles. When they're done, you flex them around some more and realize that they are now basically like thumbs. You have thumbs on your feet!
"Wait, WHAT?!" you exclaim, experimentally making gestures and fists with your new foot-hands. As if in answer to your question, thick black fur like your tail has starts spreading up your legs and over your arms, even on your belly and chest. You feel yourself getting compressed somehow, and you look around to the other animals to notice that they all seem bigger than before. You're shrinking. Your long, prehensile tail starts to make more sense. Your an animal with less height than a human but more opposable thumbs. You've obviously turned into some kind of monkey.
"eee eee AAAA AAAA AAAA AAA AAA !!" you screech out, and your transformation is complete.