Kenneth Catania, of Vanderbilt University in Nashville, recently filmed some electric eels leaping up to deliver electric shocks to "predators" -- a fake human arm and fake alligator head (video below).
Catania originally witnessed the eels jumping when he was transferring the creatures in his lab.
"I was definitely surprised," Catania told New Scientist. "This isn’t something electric eels typically do."
According to the science site, electric eels can emit both low and high voltage. They use the low charge to check their surroundings (much like radar) and employ the high charge to kill prey or for self-defense.
The electric eel has three electric organs that cover most of its body, leaving room at the front for its regular organs, such as the stomach.
"They are like giant flashlights with a lot of battery packed into their back end," Catania said.
"Sometimes up to half of their body rises out of the water," he added. "They don’t seem like dexterous animals, but they are good at it."
For his experiment, Catania put a conductive rod in an aquarium with the eels to record their electrical impulses. He also put LED lights on the fake alligator head and arm that were activated when shocked.
The higher the eels slithered up, the higher their electrical charges.
"It seems clear that the eels are actively keeping contact with their chin to try to target the object they see as a threat," Catania told the science site.
"It is a beautiful example of how the eel has evolved a fairly simple [behavior] that exploits the basic physics of electricity," added Bruce Carlson of the Washington University in St Louis.
According to Catania's study, that was published in the Proceedings of the National Academy of Sciences:
This shocking behavior likely allows electric eels to defend themselves during the Amazonian dry season, when they may be found in small pools and in danger of predation. The results support Alexander von Humboldt’s story of electric eels attacking horses that had been herded into a muddy pool during the dry season in 1800.