He had succeeded in getting his gopher, a fat, aldermanic old patriarch who had disappeared in one crunch and a gulp, and he was now absorbed in finishing off his day's feast with an occasional fat, white grub and a few sour ants captured from under stones which he turned over with his paw.
In his search after these delicacies Thor used his right paw in turning over the rocks.

Ninety-nine out of every hundred bears--probably a hundred and ninety-nine out of every two hundred--are left-handed; Thor was right-handed.

This gave him an advantage in fighting, in fishing, and in stalking meat, for a grizzly's right arm is longer than his left--so much longer that if he lost his sixth sense of orientation he would be constantly travelling in a circle.
In his quest Thor was headed for the gully.

His huge head hung close to the ground.

At short distances his vision was microscopic in its keenness; his olfactory nerves were so sensitive that he could catch one of the big rock-ants with his eyes shut.
He would choose the flat rocks mostly.