If you've never played with goop before, you have to try it.

Ingredients:

1/2 cup cornstarch
1/4 cup water
Food coloring (if desired)

Directions:
Add the water to the corn starch in a small bowl, tin pie plate, etc. Mix it together using your hands. If you need to add more water, add just a couple of drops (especially after playing with it for awhile).