I just learned about Ferrofluid today. It can do some amazing things, like this video shows. After the jump is a second video explaining HOW ferrofluid works.
From the YouTube descriptioin:
A steel sculpture with changing magnetisation is coated with ferrofluid.
The fluid is pulled in the direction of increasing flux density and forms peaks, which become smaller in higher flux density. At an accumulation of fluid at ridges, the flux density at the surface decreases. The flow and the distribution of the fluid can be observed at several characteristic locations…