Gather the following:
1 cup water
1 to 2 cups cornstarch
Food coloring (optional)
1. Pour the cornstarch in the bowl. Feel the powder. What does it feel like? What can you tell about the size of the particles that make it up?
2. Pour the water in, a little at a time, first with a spoon, but then you might want to you your hand. You want to reach a consistency which is between solid and liquid.
3. To test it...grab a potion of the oobleck. Pick up a chunk and roll it into a ball with your hands. Put the ball in the middle of you palm and don't move it. It should turn to a liquid-y substance and run off your hand.
4. Cool, right?
5. When you are finished, clean up the area with soap water.
Quickly poke at the surface of the oobleck with your index finger. Does the substance act like a solid of liquid?
Now slowly insert your finger into the oobleck. What does it act like now?
Below is a a video of how some people had A LOT of fun with this really unique substance.