Always wear eye protection during science experiments. Never handle sharp objects, open flames, chemicals, or other dangerous objects without adult permission and supervision.
Add enough milk to just to cover the bottom of the plate.
Add several drops of food coloring to the milk. If you have a few different colors, it's fun to try different patterns. Observe what's happening with the food coloring droplets. Are they moving? Staying in one place? Spreading out?
Now, take one of the ends of the cotton swab and put a small amount of dish soap on one end.
Lightly dip the cotton swab into the center of the plate and observe the changes that are occurring. See if you can think of a possible reason why this might be happening.