Again Black has left a rook loose. White’s queen has no way to attack it and give check—yet; its two possible checks at a2 and d5 both are met by Black with QxQ. But look for other checks on the board and see that the White rook has two: Rd8 and Rxg7. Examine each of them. 1. Rd8+ goes nowhere decisive after 1. …RxR, 2. QxR+, Kf7. But now ask what the board looks like after the other possibility—1. Rxg7. Black replies KxR. With the king moved, reexamine the checks that would then be possible; see that Qd7+ has been turned into a working fork that wins the rook.