Vocabulary in To Build a Fire
London employs a subtle sound technique here known as sound painting. To imitate the sound of the rustling of the bark in the man’s pocket, London describes it as “crisp,” a word which has the sound of a crunch.
Since this story's publication in 1902, "muzzle" as a noun has become more closely associated with dogs and is now rarely used as a description of a human's face. When London writes of the "ice-muzzle" that makes speech impossible for the protagonist, we're made to think of a dog that's been muzzled and of the bare animal instinct the protagonist feels to survive.