Here’s what you need:
1 cup of cornstarch
¼ cup of water
Put the cornstarch in the bowl, and add the water. Now add some more water until the mixture is runny and gooey like pancake batter.
Now reach in with your hands, take a handful, and squeeze and knead the batter like you might knead a ball of dough.
Like magic, the batter changes into a sticky but solidified ball.
Let the ball sit on your hands undisturbed. It quickly turns back into runny goo that will pour right through your fingers.
THE SCIENTIFIC EXPLANATION:
What you’ve created is the opposite of quicksand.
Some fluid mixtures, like quicksand and ketchup, get loose and runny when they get agitated. That’s why it’s better to stay calm and still when you’re standing in quicksand—you’ll sink more slowly than if you thrash around in a panic.
That’s also why ketchup spurts out so quickly when you hit the end of a glass ketchup bottle. It gets loose and runny when disturbed. The scientific name of this fluid property is called Thixotropy.
The opposite of Thixotropy is called Isotropy. Instead of liquefying when agitated, these fluid mixtures, like the cornstarch and water batter, firm up.
If you’ve walked barefoot along the edge of a sandy beach, you may have noticed isotropy with regular sand.
Strike the wet sand with your foot, and it temporarily firms up. Stand still, and your foot sinks a little bit into the wet sand.