This, the fossils in the rock, it comes in at 510 million years ago, unchanged. Astonishing thought. Now, of course, these numbers don't mean a great deal, so to put that in context, the first scraggiest, nastiest little plant didn't manage to haul itself ashore until 475 million years ago. So this thing's around when there's nothing on land.

[Q] And what is that?

And this is the... the hagfish. And you'd say, 'Well, for a primitive fish, it's quite extraordinarily sophisticated', for what I'm going to tell you, but maybe that's why it's still with us. Its jaws are so primitive... well, it doesn't really have jaws, it's jawless, but it has these opposable horny plates. And here, perhaps... or the other way around, you can see it... it has about 250 little white blobs on the side there, little glands.

Now some of them contain dried fibres and some of them contain a substance which hydrates faster than anything else we know. So the hagfish is now very interesting. Now, you're a shark, just out of primary school, or even secondary school, okay? So you're swimming along, and you see that. And you think, 'Oh, wonderful, frankfurter for breakfast'. So you home in. Bad, bad mistake.

Hagfish feels you coming, and almost instantaneously, bang, all these glands erupt, and into the water goes this mix of fibre and... well, I suppose it's sort of snot, slime, mucous. And you've got it in your eyes, you've got it in your nose. You've got it in... it's in your gills. And you shake your big head and that's another mistake, because the harder you shake, the stronger it sets. And even full-grown Greenland shark have been found floating on the surface with this snotty mucous and fibres around their heads, just like a concrete cast. You die. So that's a pretty clever trick.

And the other time they use it is when they, with their opposable horny plates... well, you know, it's not their fault, but they don't really have much taste. But if you're a drowned sailor, these things, the hagfish, it's why the trawler men hate them so. They always enter via the anus and they rasp their way up. They're after the liver, and that's the best way in, and they're in competition, because they swarm. There are hundreds of them. And to keep the other guys out, they produce a whole heap of slime. But that doesn't really work, because, as you'd say, what's the point of producing slime like that? It's going to kill you, too. It's going to set around you. No, this is the only animal on the planet, as far as we know, that's ever existed, that can tie a knot in itself and de-slime. You know, a wonderful thing to do. You wouldn't need a shower, and it passes this knot through its body and gets rid of the slime.

But this particular one is the lead guy. Up the gut to your liver and...

[Q] This is in a drowned sailor?

The only good thing about this story is you absolutely have to be dead. They're scavengers. There are other things I can tell you about, but this will only go for you if you're dead, and it goes for dead dolphins, it goes for dead whales, goes for dead anything. And very, very numerous and successful and a thing that... the trawler men just can't stand them, of course, because the sister ship of the Norlantean that I was on, she was unfortunate enough to put the nets down, go down for a mile, and got some of the bodies from that Chinook helicopter crash off the Mull of Kintyre when 45 army personnel, intelligence officers, were drowned. And they came up in the hopper and when you moved the bodies, still in their army kit, they were really swollen, and these hagfish just tumbled out, hundreds of them in every corpse.

That's part of the reason why Shetland and Orkney... the sweaters.... You know, you knit a sweater that is unlike anybody else's sweater, simply so that when your man is drowned and washed ashore on the beach, you know who it was. He's eaten out from the inside by these guys.