A fish with human teeth is known as the "nutcracker," supposedly because of its rumored affinity for chomping down on male testicles.
Terrified? That's seemingly what the media wants, based on headlines like this one from the New York Post: "This fish will eat your testicles, and it's swimming in a pond near you."
NatGeo reported that, according to legend, pacu fish (a close relative of the piranha) are a threat to men because they could mistake their testicles for their preferred food of tree nuts. (Poor fish go to bite a tree nut and get one of a whole other kind.)
Since pacu fish have eerie human-like teeth, people are especially wary of them.
According to Huffington Post, this testicle-biting rumor picked up steam after an Animal Planet "River Monsters" episode from 2011.
Host Jeremy Wade claimed he'd been told by locals that two men in New Guinea had died from the fish biting them in that unmentionable spot. "The bleeding was so severe that they died," Wade claimed. "The locals told me that this thing was like a human in the water, biting at the testicles of fishermen."
(NatGeo reported that there's little information to back up that version events.)
The myth then got some help in 2013 thanks to a "joke" that didn't really land.
CNN reported that Peter Rask Moller, a professor at the Copenhagen Museum of Natural History, warned that men "had best keep their swimsuits well-tied," after a pacu was found off the coast of Denmark.
The story was picked up around the globe, spreading word that these vegetarian fish had it out for men.
CNN reported that Moller later clarified he was kidding, saying, "It is very unlikely that you would actually meet one here and that it would bite you."
But it was a little late by then. Pacus would forever be tied to castration rumors.
The truth of the matter is that the "nutcracker" nickname is about literal nuts.
Larry Hajna, from the New Jersey Department of Environmental Protection, told USA Today that pacu fish eat nuts and fruits that fall into the water.
So, they have teeth to crack those open.
"Stories that it eats certain parts of the male anatomy are greatly exaggerated," Hajna said.
Piranha researcher William Fink echoed that sentiment to CNN, noting that human testicles and nuts dropping from trees are not easily interchangeable for these fish. "The nuts they're eating, the fruits they're eating, are splashing down from above, and humans don't act like that when they're swimming," Fink said.
While the rumors that these fish are actively attacking and killing men are seemingly unfounded, there has been one reported pacu attack on a male's nether regions. Snopes reported that the National Fisheries Authority of New Guinea investigated a 2001 incident and determined that "only one person was attacked on his private part" and that no deaths were recorded.
In any case, the chances you even find yourself near this fish, let alone in danger of being bitten, are quite unlikely.
They're native to South American waters and only introduced into American waters when irresponsible aquarium owners dump them, per NatGeo. The outlet also reported that pacu researcher Zeb Hogan ultimately wants people to know "[these fish] are not dangerous to humans." Another NatGeo article reported that even if you do find yourself in the water with a pacu, fear not.
They're afraid of humans and will avoid you.
But, if the idea of a fish with human teeth is still giving you nightmares, you can make that worse with our list of 18 toothed fish. Maybe the only way to get over the fear of fish with teeth is to face it head on? (Especially now that you know your testicles are just fine.)