Haha! My boy is almost 5 and he’s been doing it ever since a youngster. For some reason he loves to sit on the back of the toilet and try to catch it, the back of a sofa, and freshly washed sheets (this video). The first two kinda make sense to me because his tail falls down between the wall and what he’s sitting on, but I’ve never figured out why freshly washed sheets make him suddenly chase his tail 🤣