A multi-headed serpent
The hydra, a beast from Greek mythology, has multiple heads. If one is cut off, two more will grow in its place. This is based on the Hercules legend, with some texts saying that it was a many-headed water dragon, living it the swamp of Lerna, that would grow two new heads when one was cut off. The legend actually refers to a water fountain that sprouted new outlets when one was blocked.The hydra is sometimes confused witht the hydros and the hydrus.