Kenneth C. Catania, a biologist at Vanderbilt University, wanted to get a sense of just how big a jolt an electric eel can deliver. For a study in Current Biology, he allowed one to attack his own arm.

When confronted with prey or a threat, an eel transforms into a Taser-like shocking apparatus. It sends electric pulses through the water that, in succession, can paralyze its prey. When large, threatening animals get too close for comfort, eels can wrap around the intruder or leap up to create a direct electric circuit. But what was that circuit like?

Catania solved each variable of the circuit with traditional tools for measuring electricity. But working out the final variable — the resistance of a human arm — required a more creative, daring, approach.

When the eel leapt out of a tank of water and rested its head on Catania's arm, electricity flowed from the head, to his arm, to the water and back to the eel's tail to complete the circuit. To measure this flow he stuck his hand in a plastic container with exposed metallic tape on the inside and outside connected to a wire. The same electricity that flowed through his arm would also flow through the wire — and that he could measure.

Catania experienced about 10 shocks during the experiment and was able to use his numbers to extrapolate what kind of shocks eels of any size could deliver. A large eel, he said, could paralyze you.