What turns his wail of terror and hurt into one of triumph

That would be the cub,

"They surrounded the cub and laughed at him, while he wailed out his terror and his hurt. In the midst of it, he heard something. The Indians heard it too. But the cub knew what it was, and with a last, long wail that had in it more of triumph than grief, he ceased his noise and waited for the coming of his mother."