why did general smile after he blew the smoke ring into the air towards rainford's hiding spot.

The General smiled because he knew where Rainsford was hiding.

But the sharp eyes of the hunter stopped before they reached the limb where Rainsford lay; a smile spread over his brown face. Very deliberately he blew a smoke ring into the air; then he turned his back on the tree and walked carelessly away, back along the trail he had come. The swish of the underbrush against his hunting boots grew fainter and fainter.