Milk Fireworks

Pour enough milk into a pie plate to cover the bottom.

After the milk has stopped moving, place drops of different colors of food coloring in the milk.

Dip a toothpick in dish soap and then touch it to the middle of the milk.

Why:
The food coloring mixes with the water in the milk.  The soap is attracted to both the fat and the water in the milk.  When you add it to the milk, it immediately begins to grab those parts, which results in a lot of mixing and movement, which, thanks to the food coloring, you can see. 

The soap also breaks the water's surface tension, allowing all kinds of movement to occur.

 These pictures were taken using 1% milk - try it using whole milk, with more fat molecules for the soap to grab onto and see what happens.