In this demo you will learn how to listen for collisions.
When one of the other fish collides with the blue tang, the blue tang says "Watch where you're going." If the blue tang collides with one of the other fish, he says "Excuse me."
After watching this video, you should create a similar movie. Create a scene with two or three objects. Make it so the user can drag them around and reposition them. What will you do when they collide? Use your imagination to create an interesting game.