Not wanting to be stuck on a bench with no legs, you decided you'd better get down now while you still had the chance. You lowered yourself down carefully, making sure to give your new tail plenty of room to stretch out far behind you across the chamber floor. Your remaining human skin gets itchy and you start to scratch it. Your skin starts to crack, revealing even more dry-but-slimy-looking scales underneath. This is really starting to get freaky!
Something feels funny in your mouth, and you stop scratching a moment. Your tongue feels thin, and flexible in a way you don't quite recognize. Thinking you have some idea of what's happened, you stick out your tongue as far as it will go and then start flexing it up and down. Cool! You've finally got your snake tongue! When you flex it upward, it reaches higher than your forehead, it's so long and widely forked. Your tongue is almost jet black, which you decide is going to be hard to get used to. Drawing it slowly back into your mouth, you notice strange tastes coming back along with it, stimulating a couple of odd pits just behind your upper lip at the front of your mouth. It's like having a whole other olfactory sense right inside your mouth, and its very sensitive: you're not sure whether to describe yourself as tasting the air or smelling your tongue. It kind of feels like a mix of both.
The strongest taste or scent your tongue has brought back with it is one which is very familiar, like it was always there just beneath your conscious awareness if you'd ever bothered to pay attention. It's your own scent, or rather it's your human scent. You could also pick out another human scent, that of the cashier. The air also had an earthy, scaly flavor to it, representing your new snake self. There were lots of other weaker tastes/scents belong to diverse humans and animals that were harder to identify because they were in here days or weeks before. Since you really aren't used to getting such a massive upload of information from your mouth, you wait a few seconds before you try sticking your tongue out again. Tasting the air again, you can now smell the various remnants of people who came into this room and changed into animals before you. You can also smell that your human skin is getting dry, but of course you could already feel and see it wrinkling up and getting ready to come off.
Deciding you'd better take off the rest of your human skin while you still have arms, you go ahead and start peeling the flaky stuff off. It comes off fairly easy even in spite of your weakening arms, and it feels so good to let your new scales greet the fresh air from underneath it. It's truly bizarre taking off the skin of the human you once were. It's something far more intimate and exposing than taking off your clothes was. Your old skin almost looks like a corpse, your corpse, as though you were dead (you suppose in some sense you are). It's almost like you were an alien the whole time and were never really human, and now you're finally throwing off the farce. You know this isn't the last time you'll be shedding your skin, but it is the last time you'll ever see your human hair or what's left of your human face. You wonder if you should throw it down the incinerator shoot like your clothes; you decide it would feel wrong somehow, and you don't think you have the arm strength to open up the shoot anyway.
You eventually have to look away at your old skin in disgust; staring at that torn, crinkled mockery of your human self is gross and just too creepy. It's also getting harder to hold yourself in a sitting position. Your arms and legs hold you up on all fours but a little longer, but soon they're gone, and you're left with your belly on the ground. A few more skeletal jolts go through your body from nose to tail, finishing up the shape of your new form. Your torso stretches and thins until its almost impossible to tell apart from your tail, and the front of your face bunches up into a recognizalble snout shape. Your eyes get split apart as your muzzle expands, and your left staring almost sideways with a wider field of vision. A couple of pits open up near your nostrils, giving you the sense that certain things around you are warmer than others. The warmest of all is the cashier; looking at him is like turning your face to a fireplace, because he's still warmblooded. Cool! You'd almost forgotten snakes could do this.
Realizing that you were going to have to use this body to get around without limbs, you decide its time to try to make yourself go. Remembering how it felt to send waves through your tail, you start sending some all the way down the length of your body from your neck all the way down to your faraway pointed tip. Your body is now thrashing aimlessly in the chamber floor. If only you could get your weight centered right, you could probably control your direction. Sure enough, you soon find yourself moving forward, and you keep sending pulses down your length body to keep up the pace. Then you quicken the pace. Then you make a turn.
'I'm doing it!' you think proudly, 'I'm slithering! I'm a snake!' You're relief that you can actually use your body and don't seem to be having too much trouble doing what a snake does would have warmed your heart if you still had warm blood in your body. It feels a bit chilly to feel your body returning to room temperature having lost the ability to thermoregulate itself.
The old man has left the little room behind the plastic window. You can't see him anymore, but you can trace his heat signature traipsing around the corner, into the hallway, toward the chamber, presumably coming to retrieve you from this stuffy metal room. You can't wait, your ready to get out of here and start living your new life as a snake.