Most of the men choose to hunt. However, if they choose not to, they are turned over to Ivan. In the text, Connell says,
"Oh," said the general, "I give him his option, of course. He need not play that game if he doesn't wish to. If he does not wish to hunt, I turn him over to Ivan. Ivan once had the honor of serving as official knouter to the Great White Czar, and he has his own ideas of sport. Invariably, Mr. Rainsford, invariably they choose the hunt."
They are given a knife and some food, so they think that they can survive. Zaroff is too good, though, because he has not yet been beaten in his new hunting game.