The Hydra was at last killed. Herakles cut off the immortal head and buried it under a heavy stone in the road. He dipped his arrowheads in the Hydra's poisonous blood. They became deadly. Back in Tiryns, Eurystheus would not count this adventure as a Labor because Herakles had had his nephew's help. He added another Labor to the list. Hera set the crab in the sky as a constellation. The river Anigrus in Elis stank because the Hydra's poison was washed from the arrows Heracles used to kill the centaur Nessus in its waters.