If you know anything about horror movies, the first thought running through your mind after reading that headline is probably of razor-toothed little piranha fish zooming between the legs of blissfully ignorant swimmers. But the Pacu fish is different, and its teeth are compared to those of humans.
The Pacu is primarily found in the Amazon and can weigh up to 55 pounds; their teeth assist them in grinding up nuts (the kind with shells) and seeds. But some locals in Papua New Guinea have reported that two men were killed when a Pacu fish bit off their testicles, which makes one wonder about the validity of official claims that the fish is harmless to humans. The scariest part? Two of them were recently discovered in a lake in Illinois.
When a fisherman claimed he'd caught a piranha at Lake Lou Yeager last month, the Illinois Department of Natural Resources did some investigating and found that the fish was actually a Pacu. Several days later, another Pacu was spotted in the same area. Officials say they pose no threat and were likely kept as pets before someone dumped them in the lake, but I'd imagine that any male swimmers who frequent that particular body of water will be wary of jumping in for a while.