If you were to fall into the Amazon River, are you doomed to be torn apart and eaten by piranhas? Piranhas can be pretty ferocious, and we've all seen those demonstrations where a meaty bone is offered to a school of piranhas and they go to town, churning the water until it's bloody. Teddy Roosevelt wrote about piranhas in his 1914 book Through the Brazilian Wilderness, describing how they consumed an entire cow before his eyes during his South American safari, and would likely do the same to a human. That's how the idea of piranhas as dangerous man-eaters got started, and we have plenty of gory movies to show for it. A century of research has raised questions about that demonstration, but the piranha became a terrifying symbol of the dangers of the Amazon just the same. Learn about piranhas and the danger they pose in this this TED-Ed lesson.