Milk (I find 2% or skim works the best)
1. Fill the bowl about half full of milk.
2. Let the milk settle for a few seconds. If you have time (and patience), you may want to let the milk warm up a bit.
3. Carefully place 4-6 drops of different colored food coloring into the milk.
4. Plop a drop of dish soap right in the middle of the bowl.
5. You should see a nice fun swirling of colors! Feel free to plop in a bit more soap.
What's happening is the soap is separating the fats in the milk. This causes currents to form in the milk. The currents push the food coloring around and you get some really neat swirls!