Yes, the wild-dog was inside.

Not only did he smell him, but he heard the menace of his snarl.
He looked up to Skipper questioningly.

Was it that Skipper wanted him to go in after the wild-dog?
But Skipper laughed and waved his hand to show that he wanted him to search in other places for something else.
He leaped away, sniffing in likely places where experience had taught him cockroaches and rats might be.

Yet it quickly dawned on him that it was not such things Skipper was after.

His heart was wild with desire to serve, and, without clear purpose, he began sniffing legs of black boys.
This brought livelier urgings and encouragements from Skipper, and made him almost frantic.