Posted below is an interesting video on the effects of low frequency square waveforms on cornstarch. To make, simply mix cornstarch and water, then place on a large speaker hooked up to an amplifier and a signal generator (generating around 20-30 hertz). An old stereo works great, as long as it has an aux-in. There is lots of free signal generating software at arms length, like this one. I found adding a little olive oil into the cornstarch mix makes it easier to handle, and contributes to the general quality of the fluid. Cornstarch is known as a non-newtonian fluid, more information can be found here.
For a more through video demonstration, check out this tutorial video.
Another cool video, made by one of the WonderHowTo founders, Mike Goedecke: