Oobleck is a fascinating substance that acts like both a liquid and a solid, depending on how you handle it. If you pour it slowly, it flows like thick milk. But if you punch it or squeeze it hard, it suddenly becomes firm like a solid. The moment you stop applying force, it turns liquid again.

You can make oobleck at home by mixing cornstarch and water (about two parts cornstarch to one part water). Once mixed, try this: let it pool in your hand and it will drip through your fingers, but if you squeeze your fist quickly, it becomes a hard ball. Open your hand and it melts back into goo. You can even run across a pool of oobleck without sinking, as long as you keep moving fast. Stop, and you'll sink right in.

Scientists call substances like this non-Newtonian fluids because they don't follow the normal rules that liquids usually follow. The name “oobleck” comes from a Dr. Seuss book called Bartholomew and the Oobleck, about a sticky green substance that falls from the sky. Real oobleck is usually white, or whatever color you make it, and it's a favorite science demonstration because it's so weird and fun to play with.