I remember seeing a commercial advertisement in which a hamster in a cage moved itself towards a desirable item (food or something) that its owner had on the counter by throwing itself against the side of its own cage. Would this really be possible? On the one hand it seems like there are only internal forces within a hamster/cage system. On the other hand, I can't think of why it wouldn't work. The hamster just needs to apply enough force to the side of the cage to overcome static friction between the countertop and the bottom of the cage.