One of the more useful NetHack amulets -- you'll usually want to wear this amulet or an amulet of reflection. Its function is simple: if you die, you don't die. The amulet disintegrates afterwards.

An irritating thing about these amulets is that nymphs and some other enemies are sometimes wearing them. You'll only find this out after you kill them and and you see

"Suddenly, the water nymph's amulet begins to glow...--more--"

and by then it's too late; the amulet is wasted. The only good way I can think of to get an amulet of life saving from another monster intact is to polymorph it into a worm or something else that cannot wear amulets -- the amulet would then fall to the floor and you could grab it.

Polymorphing into a metallivore and eating the amulet has no effect.