Hmm, let's see. Try something that moves. Change the density value in an object to something like 1. Maybe play around with joints too. Stick a joint where two objects overlap to connect them. Or stick a joint on an object and pin it to the background. Play with the speed setting on the joint to make the object move around. (Remember to change the density of objects to 1, or anything else other than 0, when playing around with joints.)