I had a pair of Gerbils who would spin each other around in order to let go and shoot to the top of the cage, and they'd hang off the top. Sometimes they'd hang upside down and eat lunch.

General PSA moment though: I'd highly recommend not doing what this pet store does (and most unfortunately do for some unknown reason) and get a wheel without crossbars so accidents like this don't happen in the process of a good time. Most of the time it's probably fine, like kids on an old rusty play-set or a baby in a drop-side crib, but a pouding's a pounding and under that fur there could be a scrape that results in infection if gone un-noticed. And with a glass aquarium the infection could only get worse I'd imagine. And since small rodents' nature is to not get eaten in the wild, they'll rarely show signs of illness until it's often too late.