Variation: Conduct the experiment using whole milk, low fat milk, and water in separate dishes. What worked the best?
Explanation: "You will see that the color doesn't react like it does with the whole milk. Water will get no reaction. The fat and protein molecules in the milk are changed by the soap, causing them to roll around. Once the soap molecules are mixed evenly with the fat and protein, the motion will stop." - Steve Spangler
photo via School at St. George Place