It puzzled him.

It disquieted him without alarming him.

To the new and strange smell that was in the air he was as keenly sensitive as a child's tongue to the first sharp touch of a drop of brandy.

And then, at last, a low and sullen growl came like a distant roll of thunder from out of his chest.

He was overlord of these domains, and slowly his brain told him that there should be no smell which he could not comprehend, and of which he was not the master.
Thor reared up slowly, until the whole nine feet of him rested on his haunches, and he sat like a trained dog, with his great forefeet, heavy with mud, drooping in front of his chest.