Rainsford's penultimate line comes after he has fought through the jungle to escape General Zaroff. He set traps, set false trails, and finally, finding himself trapped on a high cliff, leaped into the raging waters rather than try to fight off Zaroff's dogs. He somehow survives and gets into Zaroff's bedroom.
The general sucked in his breath and smiled. "I congratulate you," he said. "You have won the game."
Rainsford did not smile. "I am still a beast at bay," he said, in a low, hoarse voice. "Get ready, General Zaroff."
(Connell, "The Most Dangerous Game," fiction.eserver.org)
Rainsford's line recalls both his hunting experience and his knowledge of Zaroff's philosophy, that the strong live to rule over the weak. Rainsford has won Zaroff's game simply by surviving, but he knows that Zaroff will never let him off the island alive, and that he would have trouble either escaping of his own volition or stealing Zaroff's boat. Therefore, although he has beaten the hunt, he is still "at bay" against Zaroff, and needs to defeat him directly in order to survive. Rainsford's will to live, especially when pitted against a man who he deems immoral, is a stronger force than Zaroff's desire to hunt.