The Water Serpent. Hydra is a beast with the body of a hound and 100 serpentine heads. It also had poisonous breath and was so hideous that it caused most people to die of fear from simply seeing it. Hercules was to kill this monster. When he started to fight it, every time he cut off one of the heads, three grew back in place of it. Seeing this was getting him nowhere, he had his charioteer, Iolus, burn the stump each time he cut off a head, which prevented the heads from regenerating.