Strange name, strange substance. Oobleck defies Newton's third law of motion (for every action, there is an equal and opposite reaction): if you pour oobleck it behaves like a liquid, but if you hit it, it behaves like a solid. In other words, you could slowly immerse your hand in it (would be liquid), then try to pull your hand out again quickly and you'd have trouble (would be solid)!
Needless to say, we had heaps of fun!
See the Oobleck recipe here if you want to try it yourself. ~L.