For instance, there is the hagfish, an eel-shaped creature with three hearts, one of which is nerveless. Its mouth is simply a round hole. It has teeth on its tongue and a single nostril. The hagfish dwells on the ocean bottom, usually half buried in the mud. This fish secretes so much slime that if a ten-to-fifteen-inch (25-to-38-centimeter) hagfish is placed in a small bucket of water and then agitated, within a few seconds it is possible to lift out the entire contents of the bucket as one great blob of slime. The flexible hagfish can also tie itself into a knot. For what purpose? So that it can apply greater leverage to a dying fish in order to penetrate it with its rasplike tongue. The slime also makes the hagfish a slippery, elusive creature to handle. But by pulling itself through the knot it can wipe off its own slimy coat. This clears excess slime away so that it does not block vital gill openings.

[Picture on page 19]

The fish that can tie itself into a knot