| Quote #1
At the man's heels trotted a dog, a big native husky, the proper wolf dog, gray-coated and without any visible or temperamental difference from its brother the wild wolf. The animal […] knew that it was no time for traveling. Its instinct told it a truer tale than the man's judgment. (6)
The dog is not fully domesticated, which means that it's a lot closer to wild than say, a golden retriever. This isn't some dog to walk down the street on a leash. This thing might do what you want it if you crack a whip enough times, but it's not going to be your buddy. More importantly, the dog's primitive instincts give it an awareness of the wilderness that is superior or "more truthful" than the man's fancy-pants sense of judgment.
| Quote #2
The dog did not know anything about thermometers. Possibly in its brain there was no sharp consciousness of a condition of very cold such as in the man's brain. But the brute had its instinct. (6)
The dog's instinct goes beyond the measurements of human thermometers, which are basically just something we've made up to communicate coldness to one another. From instinct's point of view, there's nothing really true about the measurements of thermometers. They are simply an arbitrary, meaningless way of talking about coldness, which pretty much speaks for itself when your spit freezes midair.
| Quote #3
[The dog] experienced a vague but menacing apprehension that subdued it and made it slink along at the man's heels, and that made it question eagerly every unwonted movement of the man as if expecting him to go into camp or to seek shelter somewhere and build a fire. The dog had learned fire, and it wanted fire, or else to burrow under the snow and cuddle its warmth away from the air. (6)
Even though the dog relies mostly on instinct, it's still capable of learning from its experiences. For example, the dog probably wasn't born liking fire, but after being with the man for a while, it has learned that fire can make it comfortable on such a cold day.