It's called Non-Newtonian Fluid. If you've never heard of it, you're not alone, but the results are fun and amazing.

A few years back engineering students at Lamar University did a little experiment. They mixed two parts cornstarch to one part water.

If you stand this this concoction you'll sink like you're standing in water. But, if you walk, run, roll, or dance on it, well, you have to see it to believe it.