Answer: As soon as Hercules cut off one head, Iolaus would cauterise the wound with a flaming torch so that nothing could grow to replace it. After removing the Hydra immortal head, Hercules buried it under a large rock. Then he collected the monster's poisonous blood.
Explanation: In the canonical Hydra myth, the monster is killed by Heracles (Hercules) as the second of his Twelve Labors. According to Hesiod, the Hydra was the offspring of Typhon and Echidna. It had poisonous breath and blood so virulent that even its scent was deadly.
