NASA article on studies taking place onboard the International Space Station about fluids that may one day flow through the veins of robots and help buildings resist earthquakes. Known as magnetorheological (or "MR") fluids, they harden or change shape when they sense the presence of a magnetic field.
You can make some of this exotic stuff at home. Just mix some powdered iron filings with a thick liquid like corn oil, and presto: a simple MR fluid. Hold a magnet nearby and the bits of iron will line up end-to-end; they form a rigid lattice that stiffens the mixture. Take the magnet away and the fluid will relax again.
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