Hydra is a 9 headed snake. If you cut off 1 head 2 more grow back. The breath of the hydra is so poisonous that it could kill a man just by inhalation. Heracles nephew Iolaus, who would cauterize each stump when Heracles chopped off a head, stoping the regrowth of two heads. Because the last of the heads was immortal, Heracles was forced to bury it under a large boulder.
