Researchers at Harvard have built a robotic prototype of a stingray. Its skeleton is made of gold, but its novelty is the tissue: two hundred thousand rat heart cells are embedded in a rubber layer, similar to the gel used for breast implants. This artificial ray fish responds to light cues for its propulsion. The scientists created the robot to understand better cardiac behavior, as the movements of the stingray actually mimic heartbeats. “It turns out the musculature in the stingray has to do the same thing as the heart does: it has to move fluids,” said lead researcher, Prof. Kevin Kit Parker of Harvard University. Regardless of the insights the experiment may yield, the big questions are unrelated to the study’s goal. They have created a half-robotic, half-living creature, one that invites us to question if life is simply a body connected by tissue, blood, and the nervous system. Each of these components can be synthetically replicated today.