In 1999, Yoseph Bar-Cohen of NASA's Jet Propulsion Laboratory challenged the engineering world to an arm-wrestling contest. Sort of, anyway. He doesn't plan on participating himself, and the arm, which will face off against a human opponent of middling strength, has to be robotic. The catch is, he's not asking for your standard metallic appendagethis robotic arm must be built with electroactive polymers (EAPs).