Robots typically rely on batteries to get power, but they may soon have to do little more than nibble on another material to start moving. Chinese researchers have developed simple liquid metal machines (not shown here) that zip around if they "eat" aluminum and other substances that produce electrochemical reactions. It's not possible to directly control their movement, but they closely mimic whatever space they're in -- you can propel them through channels, for instance.
These amorphous machines aren't blisteringly fast. Right now, chewing on metal lets them move at about 2 inches per second for over an hour. It's doubtful that you'll see a nimble, Terminator 2-style shapeshifting android any time soon, then -- perhaps thankfully -- but one of the basic ingredients for that kind of liquid robot is now in place.
[Image credit: Shelley Brunt, Flickr]