Whoa. This new video showing piranhas being fed in a Brazilian river is absolutely horrifying.

As terrifying as this video appears, piranhas are rarely dangerous to humans. But as University of Nevada biology professor Zeb Hogan explains in National Geographic, they can be dangerous if they're trapped in a backwater without food. And as demonstrated in this new video, these piranha are as aggressive as they are because they're likely being regularly fed by people; when they congregate like this, they act just like they would if trapped in a small pool.

[ NatGeo ]