Maurizio Porfiri wants to build robots that can herd fish like sheepdogs. Sound fishy? He's farther along than you might expect. A few years ago, Porfiri, a mechanical engineer at the Polytechnic Institute of New York University, discovered real fish would mill about and follow his robotic fish. And since then, he's been trying to understand why. In a recent study, he found that how the robot flaps its tail seems to be part of the secret to being a leader of fishes. It's not about how the robot looks, but how the robot makes fish feel.