Hercules (Heracles) and the Hydra: Mythology, Second labor

This was the second task that Hercules had to undertake to atone for his sins. The Hydra was a terrible nine-headed water serpent that lived in the swamps of Lerna and guarded the gates of the underworld.
The Hydra had nine heads. Eight of the heads were mortal, and the ninth head, surrounded, by the other eight, was immortal. However should one of the mortal heads be removed, two would grow in its place. The Hydra also had an obnoxious and poisonous breath.
The Hydra would devour cattle and other livestock in the surrounding areas, and in general, terrorize the locals. To solve this problem Hercules was sent off to kill the monster.
Hercules took his nephew along with him, Iolous, who was an expert charioteer and Olympian.
Before Hercules could kill the Hydra, he had to kill a giant crab, sent by Hera to make things more difficult. He killed the crab with his club. The crab was rewarded with a place in the constellation, Cancer, by Hera for services rendered.
To flush the Hydra from hiding, he shot a number of flaming arrows into its lair.
Hercules soon found out that it was impossible to kill the beast with a club, his preferred weapon, and took a sword, (some sources say sickle), covered his mouth with a cloth, and chopped the heads off one at a time. His nephew then cauterized the neck wound with a flaming torch, so that no further heads could grow.
After a long struggle the eight mortal heads were removed, leaving the immortal head. This was chopped off and buried under a large and heavy stone. (If the head was immortal, why would this help? Just to keep it out of the way? Somewhere I read that this head came back later to cause problems..will find out in due course)
Hercules then dipped the points if his arrows in the poisonous blood of the hydra, (some sources say gall), for future use.
The interesting part about this story is that it was seen as incomplete, as he had help from his nephew, and did not undertake the task on his own.
Some sources maintain that the original tasks set were increased, to make up for the slip-up.
Image from Wikipedia.:
(Hercules from Roman Mythology and Heracles from Greek. If you do a net search use both, different range of hits)
First Labor, the Nemean lion