Autotomy is cool shit. There is no denying the fact. If you're a prey animal (as most species on the planet are) and something gets in the mood to snack on you, you're in trouble. If that something gets a hold of you, you're pretty much screwed. Animals which practice autotomy, however, have learned that sometimes giving the finger to your would be diner can be a brilliant ploy.
Autotomy is the ability of an animal to "drop" a body part in response to danger, often followed by the regrowth of the lost bits. Generally this stimulus comes in the form of a predator grabbing the part in question, but in the case of some autotomic systems, can be inspired by threat alone.
The most known of autotomic systems is, by far, the lizard tail. Contrary to what many seem to believe, not all lizards can drop their tails, and fewer still can regrow them. Many geckos and skinks are capable of severing their tail with only the threat of danger, while most iguanid species are much less likely to, and require a good deal of tugging before the tail will break. The tails of lizards with true tail autotomy have nerve reflexes that cause the tail to flail wildly after being separated from the body, hopefully distracting the predator long enough to allow the tailless lizard to flee. The lizards accomplish the break through muscular action that breaks a vertebra while sealing off the artery in the tail.
A lesser known method of autotomy found especially in geckos is skin autotomy. When grabbed, any portion of the gecko's skin easily sloughs off, allowing the somewhat more naked lizard to flee to safety.
Of course, autotomy isn't unique to lizards. Spiders do it with their legs, as do phasmids and likely many other insects. Crabs, starfish, and octopuses can also drop limbs. Most surprising of all is that gerbils possess the ability to drop their tail in a similar fashion to lizards, although they lack the specialised ability to wilfully drop the tail, and have to make do with a stump for the remainder of their lives.
Honey bees, as we're all aware, autotomise their stingers after using them, and true to lore they die shortly after. They're kinda missing the point.