Pour the milk into a bowl and add food coloring.
Then dip a cotton swap in the soap and dip it into the milk to see what happens. There are YouTube videos that show how to do this. I have to admit that I didn’t get it when we did the experiment, and we added the soap to the milk first. Oops. The results were still very pretty, and my children loved it. My daughter is sitting on my lap looking at these pictures while I’m typing and saying “Milk! Neat!”
Luckily there is still some rotten milk in our fridge, so we are going to try this experiment again today. Add the soap last!!