"...Fenrir grew at an alarming rate, however, and soon the gods decided that his stay in Asgard had to be temporary. Knowing well how much devastation he would cause if he were allowed to roam free, the gods attempted to bind him with various chains. They were able to gain the wolf’s consent by telling him that these fetters were tests of his strength, and clapping and cheering when, with each new chain they presented him, he broke free.
At last, the gods sent a messenger down to Svartalfheim, the realm of the dwarves. The dwarves, being the most skilled craftspeople in the cosmos, were able to forge a chain whose strength couldn’t be equaled; it was wrought from the sound of a cat’s footsteps, the beard of a woman, the roots of mountains, the breath of a fish, and the spittle of a bird – in other words, things which don’t exist, and against which it’s therefore futile to struggle. Gleipnir (“Open”) was its name.
When the gods presented Fenrir with the curiously light and supple Gleipnir, the wolf suspected trickery and refused to be bound with it unless one of the gods would lay his or her hand in his jaws as a pledge of good faith. None of the gods agreed, knowing that this would mean the loss of a hand and the breaking of an oath. At last, the brave Tyr, for the good of all life, volunteered to fulfill the wolf’s demand. And, sure enough, when Fenrir discovered that he was unable to escape from Gleipnir, he chomped off and swallowed Tyr’s hand" - -