Spoon cornstarch into mug. Add water and stir. It should be difficult to stir, even when water and cornstarch are fully mixed. Color your magic mud. Don't add too much food coloring or your mud will become runny. If this happens, add a little cornstarch until the mud feels like it did before adding the food coloring. Squeeze a small quantity of magic mud between your fingers and roll it into a ball or sausage. What happens
