Piranhas

When American President Theodore Roosevelt visited Brazil, Brazilian fishermen set up an incident in which a cow was consumed by piranhas. The locals blocked off part of an Amazon tributary with nets and dumped hordes of starving piranhas into it when the adventure-loving Roosevelt explored the region on a hunting trip. A cow was tossed into the river, setting off a wild feeding frenzy that quickly reduced the carcass to bones—the "instant skeleton" now associated with piranhas.
Roosevelt would later present the piranhas as vicious creatures in his 1914 book Through the Brazilian Wilderness, indicating that
They are the most ferocious fish in the world. Even the most formidable fish, the sharks or the barracudas, usually attack things smaller than themselves. But the piranhas habitually attack things much larger than themselves. They will snap a finger off a hand incautiously trailed in the water; they mutilate swimmers—in every river town in Paraguay there are men who have been thus mutilated; they will rend and devour alive any wounded man or beast; for blood in the water excites them to madness. They will tear wounded wild fowl to pieces; and bite off the tails of big fish as they grow exhausted when fighting after being hooked.
But the piranha is a short, deep-bodied fish, with a blunt face and a heavily undershot or projecting lower jaw which gapes widely. The razor-edged teeth are wedge-shaped like a shark’s, and the jaw muscles possess great power. The rabid, furious snaps drive the teeth through flesh and bone. The head with its short muzzle, staring malignant eyes, and gaping, cruelly armed jaws, is the embodiment of evil ferocity; and the actions of the fish exactly match its looks.