It doesn't have a brain or a heart, and its walk is a little like the scarecrow's. But a little, headless, armless, trunkless, two-legged robot developed at Cornell University can walk, wobble, hobble, limp, stride, and stagger--even though it can't stand still without falling over. Made of plastic Tinkertoy parts and a few odds and ends, the robot remains stable while in motion, giving mechanical engineers new insights about how humans walk. Michael J. Coleman, a lecturer in mechanical engineering at Cornell, says the little worker, by using gravity on a gentle slope, "performs repeatable, chattering, human-like steps without falling over." Coleman stumbled on the walker's design while preparing for his doctoral defense. "It is one of the few devices of any kind that is dynamically stable near a statically unstable configuration and doesn't have fast spinning parts," says Andy Ruina, director of the Human Power, Biomechanics and Robotics Laboratory at Cornell, who assisted Coleman. The Tinkertoy device consists of two green rod legs bottomed with rounded yellow feet into a red crossbar hip, along with several orange washers and green hinges. To stabilize the toy, Ruina added low-lying red and yellow outriggers weighted with steel nuts off each foot to lower the centers of mass. He further fine-tuned the toy by rounding out the flat spots of the Tinkertoy wheels with flexible brass strips. Soon, the hand-sized gadget was tottering down a gentle slope, tilting from side to side, but steadily walking on and on and on. E-mail SSL4@cornell.edu or.