How do you determine whether a creature is immortal? In this animated video, Radiolab host Robert Krulwich explains why, after observing hydra for just a few years, one researcher suggested that the animals might live startlingly long lives.

Krulwich produced this video with Adam Cole, and talks a bit more about the research on his soon-to-be-concluded blog, Krulwich Wonders. It's just one example of how Krulwich's online work has been such a treasure.

[via Vimeo Staff Picks]