I used to have a bunch of pet gerbils, and I liked to put one in the little plastic running exercise ball and then it would get near the stairs and go on a really bumpy ride down to the first floor of my house. That was real mean, and it always made them poop a bunch of green slimy shit. It didn't permanently screw up the gerbil, it continued to mate and have a lot of babies, but I eventually got rid of all of them because they smelled everything up and were a pain to maintain.