This isn't just any old mobile: it's animated! The smaller Leefishes swim (or rather spin) clockwise and the larger Leefishes swim counter-clockwise. Unless you tell them to swim backwards, that is - they can do that, too. They won't automatically start swimming when you place the mobile, though, because they're polite like that. Also, when you feel they need some rest, just tell them to stop swimming and they will.