Martin Frey, a Munich, Germany-based experimental interface and interaction designer, has developed SnOil, a physical interactive display that utilizes ferrofluid, a liquid that reacts to magnetism. Frey has integrated SnOil with classic arcade game Snake (get it? snake + oil = SnOil) to illustrate game actions via the ferrofluid display. Check out his video here.
SnOil makes use of the ferrofluids magnetic sensitivity to selectively position and shape the fluid. This is done by electromagnets, which enable the appearing and disappearing of a magnetic field by switching the flow of an electric current.