Using water with a bit of food colouring, add it to some cornflour (maize starch) and stir around. The mixture becomes a non-Newtonian solid, meaning it acts differently than normal (Newtonian) solids. This means that it needs more pressure than normal to be a solid that we are familiar with.
Why?
If you could check out cornflour up and close you would see that the powder is made up of particles that are relatively big with edges that are jagged and uneven. When you slowly move the slime with not much force, the slime acts like a liquid as the particles have space to move around each other. However if you add more force, the jagged bits get snagged on one another and the slime acts like a rock. Once you stop stirring it quickly, the particles can slide past each other again, so the slime acts like a liquid.
