Milk is made up of minerals, proteins and fats. When the dish soap enters the milk the fat begins to break up. The soap molecules run around and try to attach to the fat molecules in the milk. Normally this process would be invisible to you, but the food coloring helps you to see all of the movement taking place. Press another dish soap covered cotton swab into the milk and see if there are any more fat molecules that haven’t been found. If you still see movement, there were still some fat molecules on the loose!
