White has a queen check to explore in Qe8. It might prematurely be dismissed as impractical, since the Black queen guards e8 and the rook at d7—the possible target of the double attack—is guarded by both the queen and the b6 knight. But pick one of those problems and play with it. The rook can’t be exchanged for a loose target as in the previous section, but ask whether either of its guardians might be taken and with what consequences. Indeed White’s rook attacks the Black knight, so walk through the capture, recapture, and resulting position in your mind’s eye. If 1. RxN, then 1. … QxR—and now the rook at d7 is loose and the e8 square is left loose as well. White takes the rook with the queen fork Qe8+, winning a piece.
Notice how a single capture and recapture can have a terrific impact on the board, here creating a double attack where none had seemed possible. It shows why looking at exchanges is another good place to start your interrogation of a position. Here, for example, you might have begun with a look not at Qe8+ but at RxN. The important point then is to follow up by imagining the board as it would look afterwards and re-asking routine questions: e.g., might a check then be combined with an attack on a loose piece?