Sure, later on you get beach balls too, but Cat Cat Watermelon Beach Ball wouldn't have made for as catchy a title.
So, Cat Cat Watermelon then. You stack these objects on top of each other. There's some simple physics, too, and the joy comes from pushing your teetering tower of cats and watermelons to the very edge.
Careful though, one cat (or watermelon) overboard and it's game over. Cat Cat Watermelon [Lexaloffle]