Why are piranha fish so dangerous?

Piranha Fish

In South American rivers swims one of the world’s most dangerous fish—the piranha.  This savage fish is only ten or so inches long, but its teeth are so sharp and its jaws are so strong. 

It can chop a piece of flesh from an animal or a human as neatly as a razor. Piranhas often travel in schools of several hundred. 

Their diet usually consists of other fish.  But if an animal happens to be in the water near a school of hungry piranhas, they attack and devour it instantly.  Animals as bit as a horse have been eaten down to a bare skeleton in only a few minutes. – Dick Rogers