That Ivan will somehow help the "prey" revolt.
That he will break down if hunting isn't fun any more.
That Rainsford will not be a challenge.
He is more afraid of Ivan than of Zaroff.
He is certain he can outwit the general.
He wants more time to think about how to get off the island.
He really doesn't have a choice.
The general has no telephone and knows that Rainsford will be locked in the cellar forever.
The general is confident in his own abilities to hunt and kill, and therefore Rainsford will be dead.
The general knows he will eventually convince Rainsford to keep quiet.