Answer: A piranha
In order to play with the young gorillas, Tarzan was dared to pull an elephant hair from an elephant's tail. Tarzan swam up behind the elephants. Tantor, a young elephant, tried to warn the others that there was something behind them but they didn't believe him. When Tarzan pulled the hair from an elephant's tail, the elephants went crazy and began to charge. The leader of the gorillas, Kerchak, saved a young gorilla from being trampled by the elephants. Tarzan was admonished by Kerchak for what he did, but showed Terk that he got the elephant hair.