You will need: 1 cup water, 1 to 2 cups of cornflour, food colouring (optional)
Mix the water and cornflour together, adding the flour a spoon at a time, and add the food colouring if using. Once it reaches the right consistency it will feel very weird – it is both a liquid and a solid! Now play with it! If you squeeze it, jab it or quickly run your fingers through it will feel solid, but if you let it ooze out of your fingers or slowly put your hands in it, it will feel liquid!
The science behind it: oobleck is a non-Newtonian fluid so acts like a liquid when poured but a solid when a force is acted upon it.