For his second labor, Heracles (Roman Hercules) had to slay the Lernaean Hydra, a serpent-like beast from the underworld that had several heads, and poisonous blood. When Heracles reached the swamp in which the creature lived, he shot flaming arrows at it, in order to bring it out to him.
As Heracles cut each head off, he noticed that two grew back in its place. Frustrated, Heracles summoned Iolaus*, who came up with the idea to used a brand to scorch the stumps of the severed heads. This would supposedly prevent the new heads from sprouting. Heracles agreed to this, and he was able to successfully slay the Hydra. Heracles then dipped his arrows into the creature's toxic blood, and he was off to his next labor.
*As a reward to Iolaus for his help, Heracles presented him with his own wife, Megara. Megara no doubt reminded Heracles of his terrible deeds, and Iolaus and Megara went on to have one child together.
