White Fang How did White Fang react to the gun?

From the text:

“Look at the intelligence of him,” Scott went on hastily. “He knows the meaning of firearms as well as you do. He’s got intelligence and we’ve got to give that intelligence a chance. Put up the gun.”

“All right, I’m willin’,” Matt agreed, leaning the rifle against the woodpile.

“But will you look at that!” he exclaimed the next moment.

White Fang had quieted down and ceased snarling. “This is worth investigatin’. Watch.”

Matt, reached for the rifle, and at the same moment White Fang snarled. He stepped away from the rifle, and White Fang’s lifted lips descended, covering his teeth.

“Now, just for fun.”

Matt took the rifle and began slowly to raise it to his shoulder. White Fang’s snarling began with the movement, and increased as the movement approached its culmination. But the moment before the rifle came to a level on him, he leaped sidewise behind the corner of the cabin. Matt stood staring along the sights at the empty space of snow which had been occupied by White Fang.

The dog-musher put the rifle down solemnly, then turned and looked at his employer.

“I agree with you, Mr. Scott. That dog’s too intelligent to kill.”