When the Huskies attacked they had a big fight. This led to the dogs to being attacked. Then one of the dogs became "mad."
Well since the dogs have been pushed extremely hard in the past couple days they need a rest. Buck on the other hand is healthy and does not need a rest. This shows that Buck has adapted to the harsh treatment.
When Buck was leading a pack of huskies to a kill a bunny Spitz took a shortcut to kill the bunny. This made buck inferior. At that moment Buck was trying to attack Spitz. Until he put Spitz to the ground. Since this happened the Huskies killed and ate Spitz.
Dave was so tired but did not give up. Since he was a husky we would not let anyone take his job away from him. So he wanted to die in his job not anywhere else.
When buck saw John Thornton dead a stream of rage went through his body. This led him to killing most of the Yeehats that killed his master. So this led to Buck slitting the throats.
Buck now runs with his "Wild Brother" This was the last thing until his final form. The Yeehats said that Buck turned into a spirit animal that takes control of that valley that John Thorton's camp was at.