Read this excerpt from White Fang. Further, [White Fang] was more directly connected with the Wild than [the other dogs]; and he knew more of its secrets and stratagems. A favourite trick of his was to lose his trail in running water and then lie quietly in a near-by thicket while their baffled cries arose around him.

Which best describes the force that motivates White Fang to run for the woods when chased?

an external force based on friendship
an external force based on setting
an internal force based on instinct
an internal force based on feelings