An anonymous reader writes "There are a few robots that do amazing things. Honda's Asimo can walk backward and climb stairs. Sega's idog can dance to music. A tougher nut to crack has been making robots walk like humans. Today, scientists introduce three humanoid striders at the annual AAAS meeting. Unlike other robots that have to power every move, these three save energy by letting gravity do a lot of the work. Like humans, they pick up their feet and just let 'em drop. Engineers say they'll inform the next generations of humanoids and also improve design of robotic prostheses for people. And hey, why not send them to Mars to look for those microbes?"