Since Rainsford appropriated his bed for the night, it is implicit but fairly clear that he "did Zaroff in." It is even stated that he couldn't remember when he had ever slept so well, suggesting that his conscience wasn't bothering him at all. And why should it? He had met Zaroff on is own terms and "won" even if it hadn't really been a fair fight. Against all odds he had managed to survive; why should he put his life in jeopardy again by showing any mercy at all on a man as cunning and cruel as the general?
Zaroff had hunted men and killed them by simple pleasure; Rainsford had simply defended himself, since even according to Zaroff, there could only be one of them left. Not to mention that by killing him, he had finally rid the island of a demoniac who "got his kicks" by making other people suffer.
In the denouement of "The Most Dangerous Game," the reader must infer what Rainsford has done. To do this, the reader recalls previous scenes and dialogue which indicate character development in Rainsford. At one point, for example, Rainsford changes from his original attitude of repulsion of General Zaroff's "game"--"what you speak of is murder"--after he himself knows what it is to be an animal at bay as Zaroff's hounds pursue him. For, at this point Rainsford has been reduced to the prey whose only thought is how to simply survive. The line "Rainsford knew now how an animal at bay feels" foreshadows his change in attitude which will affect his later actions.
So, when as Zaroff narrows in on him and Rainsford escapes into the sea, he returns with the one intention of ending this dangerous game. Apprehending his intentions, the general "
sucked in his breath and smiled. 'I congratulate you,' he said. 'You have won the game.'
I am still a beast at bay...Get ready, General Zaroff.
The general bows, saying "I see," indicating his comprehension of Rainsford's deadly intentions:
Splendid! One of us is to furnish a repast [meal] for the hounds."
The final line: "He [Rainsford] had never slept in a better bed," indicates that Zaroff is dead and a "repast for the hounds."