The costume seems to be that of a mouse, with grey fur, thin pink paws and a long tail.
Taking it to the dressing rooms, you are advised to remove all your clothes. Having done so, you examine yourself. You find that you have a lot of contol with the tail, even being able to curl it up. The costume does feel a bit tight though, and as you leave your normal clothes with the shop assistant, you feel as if it's getting tighter, compressing even.
And then suddenly you shrink to the size of well, a mouse. Instantly you are in danger from being stepped on so you scamper off, dodging peoples feet as you run out of the shop and through a fence. There you stop to catch your breath as there are no people there.
You soon find out why, though; you have wandered into one of the animal enclosures, the one belonging to the...