Observe the four White pieces lined up on the first rank, including his king and queen; and see the battery of queen and rook that Black has on the open h-file. Where does Black go from here? He examines every check. There are two: QxR and Qxg3. Qxg3+ seems safer, but QxR+ is the stronger move. Imagine White’s recapture KxQ and interrogate the resulting position. The exchange would leave behind a striking pattern: White’s king and queen would be one square apart on the same rank; Black’s rook would be ready to drop down to h1 for a classic back-rank skewer. Need Black worry that when White’s king moves, it still will be able to protect his queen? Not this time. The king will be required to leave the back rank and will not be able to reach the preferred square—e2—because one of his own pieces already occupies it. Instead the king is squeezed up to g2 (f2 is attacked by Black’s knight), leaving his queen loose and exposed to capture by Black’s rook. Black wins a rook with the sequence.