It’s no secret that electric eels stun their prey—accounts of such occurrences date back centuries. But unless you work security on the starship Enterprise, “stun” is a vague term. What really happens when these creatures attack? Until recently, biologists knew surprisingly little about the electric eel’s superpower. I was not planning to study this phenomenon, and I certainly never imagined I would offer an eel my arm in the name of science, as I eventually did. But as a professor of biological sciences at Vanderbilt University, I teach about electric fish, and when I brought some eels to my laboratory so I could obtain new photographs and slow-motion movies to liven up my lecture, I saw something so strange that I had to drop everything else to investigate.