This stuff is amazing. My boys (okay and me too) were totally taken with this goo. Oobleck defies Newton’s third law of motion–for every action, there is an equal and opposite reaction. If you quickly smack oobleck with your hand it immediately turns into a solid, instead of splashing or moving. If you slowly move oobleck it reacts like a liquid. Needless to say our oobleck took a lot of fist smacking!
(Yes, I know–that doesn’t really violate Newton’s Third Law. But it is an example of a Non-Newtonian Fluid)