Their teeth might be fearsome, but piranhas usually aren't out for your blood. UC San Diego

Piranhas are the stuff of nightmares and 3-D horror films – but some experts say the fish’s ferocious reputation is overhyped. While the carnivorous fish isn't necessarily something you'd want to cuddle with, it's not going to automatically chew you up if you step in its river.

It is undisputable that piranha attacks do happen. This past Christmas Day, officials in Rosario, Argentina reported that more than 70 people were injured by a school of carnivorous fish on the Parana River. More than 20 children were injured, including a seven-year-old girl who lost part of her finger. The culprits were reportedly not piranhas, but palometas, a close relation of the piranha, officials said.

Piranhas have also been blamed in the death of a five-year-old Brazilian girl in 2012. In 2009, a school of piranhas injured at least 15 people bathing in a river near the small town of Adolfo, about 300 miles northwest of Sao Paolo.

But most research, in fact, shows that the horror movie depiction of piranhas is overblown, according to author Richard Coniff, who specializes in animal and human behavior. The piranha's mind isn’t hard-wired to “ravenous killing machine.”

“I once climbed into a tank of hungry red-bellied piranhas at the Dallas World Aquarium,” Coniff wrote in the New York Times. “They fled to the opposite corner.”

Piranhas will get worked up if there is a high concentration of food around, Coniff says. So you wouldn't want to go to wading near highly piranha-populated areas like bird rookeries, where the fish wait to snap up fledgling chicks that fall in the water, or near docks where fisherman are cleaning their catch. (According to The Independent, the Parana River fish involved in the Christmas Day attacks may have been attracted by bait left behind by local fishermen; the five-year-old girl killed in 2012 lived in a fishing town). In most cases, a lone bather usually has little to fear.

Plus, in some stories of deadly attacks, the piranhas might be innocent. In 1987, Brazilian researchers Ivan Sazima and Sergio de Andrade Guimaraes suggested in a paper that many stories of ravenous man-eating piranhas may stem from the fish taking bites out of drowned humans, post-mortem. The pair dug up three cases in which piranhas had snacked on people that were clearly dead before the fish started nibbling.

“Some of the human deaths attributed to piranhas most probably are cases of scavenging on drowned or otherwise dead persons by these opportunistic schooling carnivores,” Sazima and de Andrade Guimaraes wrote.

U.S. President Theodore Roosevelt also had a hand in popularizing the myth of the bloodthirsty piranha, which he called “the embodiment of evil ferocity” in his 1914 book “Through The Brazilian Wilderness.” In that book, Roosevelt also recounted witnessing piranhas strip a cow down to the bone in the Amazon River. But it turns out that incident was staged; according to Mental Floss, locals had trapped piranhas in a cordoned-off portion of the Amazon and starved them for several days, before tossing in an unlucky bovine.

"It is not that piranhas lack the ability to strip people to the bone — because they could," the Johns Hopkins newsletter says. "The problem is that these fish and most other carnivores are not as horrible the media makes them out to be. Piranhas actually team up to protect themselves from predators. While their infamous feeding frenzies are real, they mostly pick on the wounded and weak."