Some very unusual things happen when you mix a little milk, food coloring, and a drop of liquid soap. The milk is more complicated than it looks. It is made up mostly of water and then equal parts of protein, fats, and sugar. The fat has been broken up and spread throughout the milk (by the process called HOMOGENIZATION) into tiny pieces of fat called globules. When the milk was first placed into the carton, it was still and did not move. Even when the food coloring was added to the milk, things were still quiet. This is because the fat globules were steady and undisturbed. When the soap hits the milk, things begin to move.
The soap breaks up the fat globules and lets them spread across the surface of the milk. As the globules break and expand, they create movement in the milk. Normally you would never notice this, but the food coloring shows how the surface of the milk moves and changes in response to the soap breaking up the fat in the whole milk.
This flowing shows how soap works. It is the same kind of thing that happens when you wash dishes or hair with soap. The soap breaks up the fat or grease and lets it to flow in the water and down the drain.