A single fundamental principle can be used to describe the way a variety of both living and engineered systems move. In each case, the system performs a desired maneuver by repeating a cyclic change in the shape of its \body". A classic example is a falling cat that wiggles its body so that it lands feet rst on the ground. The cat falls under the force of gravity, but it is the wiggling of the body that produces the cat's reorientation as needed. These body wiggles are cyclic changes in the cat's shape. Consider that at the instance of the beginning of the fall, the cat is upside down and its spine is bent forward. The cat bends rst to one side, then backward, then to the other side and nally forward again (see Figure 1). At the end of this cycle, the cat's shape is as it was initially but its orientation has changed; it has turned over so that it is now falling feet rst (Kane and Scher 1969)!