Every time two cats collide, the smaller one disappears and the bigger one gets bigger. Every time a collision happens, the first clone to get the notice of a collision sets "collider1" to its own ID, and sets "size1" to its own size. Then, when the second clone gets notice of collision, it sets "collider2" and "size2". Then it sends a "collide" message. The code to handle the collide is in the background. It compares the two sizes, then sets "collision winner" and "collision loser" to the correct clone iDs. Then it raises the "kill loser" message, and each clone compares its own ID to the "loser" and "winner" variables. It's very convoluted, and there's probably a better way to do it. If multiple collisions happen simultaneously, I'm not sure this code will actually work. But...if there are enough objects on screen to make that happen, I'm not sure anyone would notice!