Jack Costello studies how jellyfish move and feed. He dives to videotape moon jellies swimming and observes that they don't really move much. With this in mind, he seeks to answer the question: why do jellyfish spend their time swimming? And, in fact, as Costello observes, they are not really designed for making forward progress. He designed an experiment to look at how jellyfish swimming creates currents. Injecting particles into the water reveals what the jellyfish are doing: they are creating currents that bring particles to the tentacles so they can capture their prey. And each jellyfish does this differently, allowing them to capture different prey. [6:18]