Batoid fishes, which include stingrays, have served as inspiration for a bizarre robot that is a hybrid of machines and living cells. Kevin Kit Parker of Harvard University and colleagues put living muscle cells from a rat’s heart on an elastomeric body enclosing a microfabricated gold skeleton, so that the structure could mimic the undulating swimming motion of a batoid fish. The muscle cells, which were genetically engineered to contain an optogenetic molecular switch, were controlled externally via an optical signal. The artificial animal, which replicated fish morphology at the 1/10th scale (corresponding approximately to the size of a one-cent coin) including the basic fin deflection patterns of batoid fish, uses these light cues to navigate simple obstacle courses.