harum.koh via Wikimedia Commons // CC BY-SA 2.0
harum.koh via Wikimedia Commons // CC BY-SA 2.0

When Cornered, Electric Eels Rise Out of the Water to Attack

harum.koh via Wikimedia Commons // CC BY-SA 2.0
harum.koh via Wikimedia Commons // CC BY-SA 2.0

Don’t ever corner an electric eel. When threatened, the snakelike fish can rear out of the water to deliver a more powerful shock. Vanderbilt University biologist Kenneth Catania describes the behavior in a paper in the Proceedings of the National Academy of Sciences.

This is not the first time someone has reported a literal eel uprising. At the turn of the 19th century, explorer and naturalist Alexander von Humboldt wrote of a South American practice of “fishing with horses,” in which local fishermen herded very unfortunate horses into waters filled with electric eels. Frightened by the horses, the eels reportedly leapt from the water to shock them, thus exhausting all their zapping power and making them easy targets for the fishermen, who then waded in to scoop them up.

Image Credit: Robert H. Schomburgk // Public Domain

"The first time I read von Humboldt's tale, I thought it was completely bizarre," Catania said in a press statement. "Why would the eels attack the horses instead of swimming away?" 

Other modern biologists agreed: Like so many other sights described by early naturalists, von Humboldt’s leaping eels must have been a flight of fancy. 

Then, the eels proved them wrong. Catania keeps electric eels—which are not technically eels at all—in his laboratory and was studying how they hunt. To get a closer look at an eel, he’d use a metal-rimmed net to remove it from its tank.

"In hindsight, it probably wasn't the best design to use with electric eels," he said.

But that poor choice led to a surprise: “From the outset, eels regularly transitioned from a retreat to an explosive attack when the net approached," Catania writes in his paper. "They swam rapidly toward the net, followed the metal rim to the point of exit from the water, and leaped upward along the rim and handle, keeping their chin in contact while discharging high-voltage volleys. This behavior was both literally and figuratively shocking.” Fortunately, he was wearing non-conductive rubber gloves.

Still, Catania didn’t understand why the eels would leave the water instead of swimming away. He set up a series of experiments using two “attackers”: a plastic alligator head and a fake human arm covered in electrical sensors to simulate human nerve endings.

You can see the results for yourself here.

The eels, it turned out, were using the laws of nature to amplify their zapping power. When they rear out of the water and press against their target, the normal path of electrical current, which is usually distributed to the surrounding water, is replaced with a new path that goes right through the target of attack. 

"This allows the eels to deliver shocks with a maximum amount of power to partially submerged land animals that invade their territory," Catania said. "It also allows them to electrify a much larger portion of the invader's body."

But when faced with a potential predator, why do eels do shock instead of retreat? Catalina suggests that backing off often isn't an option, especially in the annual dry season, when the eels can get trapped in small pools. As he says in the video: "Essentially, what you've got there is an electric fence in the form of a fish." 

ZUMA Press, Inc., Alamy
5 Fascinating Facts About Koko the Gorilla
ZUMA Press, Inc., Alamy
ZUMA Press, Inc., Alamy

After 46 years of learning, making new friends, and challenging ideas about language, Koko the gorilla died in her sleep at her home at the Gorilla Foundation in Woodside, California on June 21, 2018. Koko first gained recognition in the late 1970s for her ability to use sign language, but it was her friendly personality that made her a beloved icon. Here are five facts you should know about the history-making ape.


Francine "Penny" Patterson, then a graduate student at Stanford University, was looking for an animal subject for her inter-species animal communication experiment in the early 1970s when she found a baby gorilla at the San Francisco Zoo. Originally named Hanabiko (Japanese for "fireworks child," a reference to her Fourth of July birthdate), Koko took to signing quickly. Some of the first words Koko learned in "Gorilla Sign Language," Patterson's modified version of American Sign Language, were "food," "drink," and "more." She followed a similar trajectory as a human toddler, learning the bulk of her words between ages 2.5 and 4.5. Eventually Koko would come to know over 1000 signs and understand about 2000 words spoken to her in English. Though she never got a grasp on grammar or syntax, she was able to express complex ideas, like sadness when watching a sad movie and her desire to have a baby.


Not only did Koko use language to communicate—she also used it in a way that was once only thought possible in humans. Her caretakers have reported her signing about objects that weren't in the room, recalling memories, and even commenting on language itself. Her vocabulary was on par with that of a 3-year-old child.


Koko was the most famous great ape who knew sign language, but she wasn't alone. Michael, a male gorilla who lived with Koko at the Gorilla Foundation from 1976 until his death in 2000, learned over 500 signs with help from Koko and Patterson. He was even able to express the memory of his mother being killed by poachers when he was a baby. Other non-human primates have also shown they're capable of learning sign language, like Washoe the chimpanzee and Chantek the orangutan.


Koko received many visitors during her lifetime, including some celebrities. When Robin Williams came to her home in Woodside, California in 2001, the two bonded right away, with Williams tickling the gorilla and Koko trying on his glasses. But perhaps her most famous celebrity encounter came when Mr. Rogers paid her a visit in 1999. She immediately recognized him as the star of one of her favorite shows, Mister Rogers' Neighborhood, and greeted him by helping him take off his shoes like he did at the start of every episode.


Koko was never able to have offspring of her own, but she did adopt several cats. After asking for a kitten, she was allowed to pick one from a litter for her birthday in 1985. She named the gray-and-white cat "All Ball" and handled it gently as if it were her real baby, even trying to nurse it. She had recently received two new kittens for her 44th birthday named Ms. Gray and Ms. Black.

Why Do Dogs Crouch Forward When They’re Playing?

Whether they're tilting their heads or exposing their bellies for rubs, dogs are experts at looking adorable. But these behaviors do more than elicit squeals from delighted humans; in many cases, they serve important evolutionary functions. A prime example is the "play bow": If you've ever seen a dog crouch forward with its elbows on the ground and its rear end in the air, wagging tail and all, then you know what it is. The position is the ultimate sign of playfulness, which is important for a species that often uses playtime as practice for attacking prey.

The play bow first evolved in canids as a form of communication. When a dog sees another dog it wants to play with, it extends its front paws forward and lifts up its behind as a visual invitation to engage in a friendly play session. Dogs will "bow" in the middle of playtime to show that they're having fun and wish to continue, or when a session has paused to signal they want to pick it back up. Play bows can also be a sort of apology: When the roughhousing gets too rough, a bow says, “I’m sorry I hurt you. Can we keep playing?”

Play between canines often mimics aggression, and starting off in a submissive position is a way for all participating parties to make sure they’re on the same page. It’s easy to see why such a cue would be useful; the more puzzling matter for researchers is why the ancestors of modern dogs evolved to play in the first place. One theory is that play is crucial to the social, cognitive, and physical development of puppies [PDF]. It’s an opportunity for them to interact with their own kind and learn important behaviors, like how to moderate the strength of their bites. Play also requires the animals to react quickly to new circumstances and assess complex actions from other dogs.

Shiba inus playing outside.
Taro the Shiba Inu, Flickr // CC BY 2.0

Another evolutionary explanation is that playtime prepares puppies for the hunting they do later as adults. Watch two puppies play and you’ll see them stalking, biting, and pouncing on one another—all behaviors canines exhibit in the wild when taking down prey.

Of course, it’s also possible that dogs simply play because it’s fun. This is a strong case for why pet dogs continue to play into adulthood. “Devoting a lot of time to play may be less advantageous for a wild species who spends much of its time hunting or foraging for food, searching for mates, or avoiding predators,” Dr. Emma Grigg, an animal behaviorist and co-author of The Science Behind a Happy Dog, tells Mental Floss. “Many domestic dogs are provisioned by humans, and so have more time and energy to devote to play as adults.”

Because play is a lifelong activity for domestic dogs, owners of dogs of all ages have likely seen the play bow in person. Wild canids, like wolves, foxes, and coyotes, tend to reserve this behavior for members of their own species, but pet dogs often break out the bow for their humans—or anyone else who looks like they might be up for a play session. Grigg says, “One of my dogs regularly play bows to her favorite of our cats.”


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