Heracles' second labor was to encounter the Hydra, a nine-headed serpent, which would grow back two heads for every one that was severed. Every time he clubbed off one of the heads he cauterized the stump so that another could not grow. A hydra is a polyp with a cylindrical body and tentacles surrounding an oral cavity and it has the ability to regrow itself from cut off parts. A hydra can also be a destructive force that does not succumb to a single effort. The Hydra is a constellation in the equatorial region of the southern sky near the constellation Cancer.