Hydras. How do they work?

From Hansard, where Michael Wood teaches us about the classics:

Before I get to those, I just do need to reflect a little bit on some of the comments that have been made in the debate this evening. The first one I want to reflect back on, and it came through a number of National Party speeches—it had obviously been produced from the research unit, and different National Party MPs were trying to use it in a slightly different way—came out in the form of an accusation that this Government was some kind of three-headed monster, or, as Sarah Dowie put it, a three-headed hydra. Well, what I just want to explain briefly, for those members of the House who didn't study classical studies while they were at school is that the thing about hydras is that they're immortal and every time you attack them they just come back stronger. That is going to be the case with this Government. [emphasis added]

Now I haven't studied classics, but I've been listening to the Greek Myths. A lot. Over and over in the car - when we're not listening to Sherlock Holmes stories.

Here's StoryNory (strongly strongly recommended if you do any kind of long car ride with kids):

Heracles’ next task was to fight another terrible creature. This one lurked in the swamps of Lerna, and it was known as the Lernaean Hydra. It was giant snake with multiple heads. If you cut off one of its heads, two more would grow in its place. It was indeed a fierce opponent. Even Heracles did not think he could fight this monster on his own. He enlisted the help of his nephew, Iolaus. Heracles fought the Hydra with his sword, and each time he lopped off one of its heads, Iolaus jumped in with a torch and burned the stump before it sprout a couple of new heads. Hera looked down on this struggle to the death, and thought, “Two humans against one monster! That’s hardly fair!” and she sent a giant crab to join in the fight. Heracles and Iolaus stood back to back and fought off both these supernatural beasts. After defeating them in battle, Heracles collected some of the Hydra’s blood to use as poison on his arrows.

He returned to Eurystheus with news of his victory, but the king was not satisfied. “You did not fight the Hydra on your own,” he said, “And so the labour does not count.” Heracles shook his giant fist at the king, but Eurystheus, who was feeling safe at the top of his tower, shouted down: “It’s no use arguing. You’ve still got nine more labours to do, Heracles. Your next task is to bring me the sacred dear of Artemis – you’ll find it roaming the hills of Ceryneia. You will know it when you see it. It has little horns, made of gold.”

So. Should I be telling the kids that StoryNory had it all wrong and that the hydra is really immortal? Are there more complete versions of the story where Iolaus's trick only delayed the creature's regeneration?

HT: Chloe Swarbrick

“The opposition has been talking a lot about the three headed hydra. I don’t know if they studied classics, because the thing about hydras is they’re immortal.” - @michaelwoodnz delivering a characteristically poetic estimates speech #nzpol

— Chlöe Swarbrick (@_chloeswarbrick) May 23, 2018