You will need:
- food colouring
- a toothpick
- dishwashing liquid
Pour some milk into a shallow bowl or dinner plate and add a few drops of food colouring in different colours.
Now dip the tip of your toothpick in the dishwashing liquid, and then into the milk. The soap will disrupt the surface tension of the milk, making the colours explode into lovely, bright kaleidoscope-like designs!