OOBLECK. This stuff is amazing. Mix 2 cups of cornstarch and 1 cup water in a bowl. To color oobleck, add a few drops of food coloring to the water before adding to the cornstarch. Takes some effort to mix the water and cornstarch. 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. I remember this stuff as magic mud when I was a kid!