I am doing a lighting design job at the Children's museum, and I looked around to see what they had around there. They have a room with a few projection screens set up, and on one of them, there is a projection of marbles. You stand in front of the projector, and move the marbles around with your shadow. They have one with butterflies, and when you stick your hand out, they land on the shadow of your hand. It is really really cool. Being a computer nerd and projection designer, I was really intrigued. If you want to check out some of the other stuff they have, check out www.mine-control.com