Megapiranha (DVD)

Piranhas the stuff of nightmares and legends. They're infamous for how fast they can devour prey, and are known to attack in groups of up to 100. National Geographic joins a team of scientists heading to the Amazon to investigate a piranha mystery of immense proportions. A fossil of a giant jaw fragment has been identified as an ancient piranha, but with a terrifying twist: The tooth belonged to a fish seven times the size of existing piranha species.