What was the cub's reaction when he encounters fire?

The cub's initial reaction is curiosity.

Suddenly he saw a strange thing like mist beginning to arise from the sticks and moss beneath Grey Beaver’s hands. Then, amongst the sticks themselves, appeared a live thing, twisting and turning, of a colour like the colour of the sun in the sky. White Fang knew nothing about fire. It drew him as the light, in the mouth of the cave had drawn him in his early puppyhood. He crawled the several steps toward the flame. He heard Grey Beaver chuckle above him, and he knew the sound was not hostile. Then his nose touched the flame, and at the same instant his little tongue went out to it.

For a moment he was paralysed. The unknown, lurking in the midst of the sticks and moss, was savagely clutching him by the nose. He scrambled backward, bursting out in an astonished explosion of ki-yi’s.