Not that I hope to ever need this information, but can a live snake be tied into a knot that it can't get out of? —Richard Payne
Well, I suppose you could do that, and then you'd have a snake that was either badly injured or dead. Fortunately, snakes themselves don't wriggle into knots they can't wriggle out of—at any rate, healthy ones don't. On the contrary: many snakes and other legless critters have an extraordinary facility for self-knotting, and can tie and untie themselves with a dexterity that would leave a sailor or Boy Scout in awe.
The knot-tying abilities of snakes arise from the remarkable combination of flexibility and muscle control that makes snake locomotion possible. Besides the familiar undulating motion, snakes also move via sidewinding, a kind of diagonal self-flinging used on sand and other low-traction terrain, and "concertina movement," used in tunnels, where the snake gathers itself into a series of close-spaced bends (suggesting a concertina or accordion), then pushes forward as it straightens out.
Some snakes, notably constrictors and pythons, have more vertebrae per unit of body length than others, and as a result can tie themselves into knots and balls, a well-named case in point being the ball python. Normally they do this for defensive purposes, sometimes hiding their heads in the middle of the tangle and remaining motionless until the predator (they hope) leaves them alone.
Other snakes tie themselves into knots to aid in shedding their skin. While some land snakes do this, it's apparently more common in sea snakes, no doubt due to the fact that they often lack a convenient source of friction to help them pull the old skin off. The snake ties itself into an overhand or figure-eight knot that it undulates down the length of its body.
Sometimes a snake will form two or more knots at the same time, which may inspire the giddy to imagine a Snake Olympics (most knots! most twists! most artistic design!). Please. Self-knotting also helps snakes scrape off skin parasites. These are animals with more basic things on their minds.
Snake knotting isn't always a good thing—it may mean the snake has come down with inclusion body disease, a distant relative of Ebola. First recognized in the 1970s, IBD is a fatal viral disorder that causes a variety of neurological symptoms in snakes, including paralysis, disequilibrium and a tendency for the afflicted snake to tie itself into knots, sometimes ones it can't undo.
Experiments have shown that snakes will knot themselves in a weightless environment. After initial thrashing, the researchers observed, the snakes "became quiet upon self-embrace"—to put it another way, they calmed down once they'd tied the knot and (literally) gotten a grip on themselves. To you or me this might sound like a good thing. Not to the scientists, who thought it "suggests a failure to distinguish self from non-self." How dare you compose yourselves, you silly reptiles—don't you know the situation calls for existential dread?
Snakes aren't the only animals with self-knotting capabilities. Several species of eel use knotting during feeding. If you're the type that gets irked by coarse table manners, make sure you never have dinner with an eel: After grabbing onto a fish with its jaws, the eel whips its body around to create a figure-eight knot, then rapidly pulls its head back through the knot. Result: swallowing, decapitation or other dismemberment of the target fish.
Probably the most creative uses of animal knotting—and perhaps also the most disgusting, but one tries not to be judgmental—are seen in the hagfish, an eel-like critter that's surely in the running for ugliest life form on earth. The hagfish is so flexible it makes snakes look arthritic, a consequence of its not having a spine. It can easily tie itself in knots when circumstances warrant.
Hagfish can use their knots as a way to dig burrows. One will position itself perpendicularly over the sea-floor mud, fold its tail into an overhand knot, and spasm itself quickly to push the knot down its body length and drive its tail into the mud. They'll use a similar tactic during feeding, using the knots as leverage to extract prey from tight spaces after they bite hold of it.
But their most common use of knotting is to avoid being eaten themselves. Hagfish are notorious for exuding huge amounts of slime, which not only makes them extraordinarily slippery but can clog the gills of predators, causing them to choke and release the hagfish or, better yet, not bite it in the first place. If that doesn't suffice, the hagfish can form an overhand knot that it slides up or down its body, pumping out slime even more voluminously, which either forces the predator to release its grip or grosses it out of existence. Connoisseurs of ickiness can find videos of the hagfish in action on YouTube; if you like tentacle porn, you'll love this.
Send questions to Cecil via StraightDope.com or write him c/o Chicago Reader, 350 N. Orleans, Chicago 60654.