The mixture of cornstarch and water to form a non-Newtonian fluid is commonly referred to as Oobleck.

If you can only make a small quantity of it, the most fun thing to do with Oobleck is to destroy loudspeakers:

Videos of Oobleck responding to sinusoidal displacement:

Anyone can make Oobleck move with a constant frequency, but the real challenge is to get it dancing to music: