Black’s king can't capture the knight or pawn because both are protected. He has to move his king, and its only available squares are f5 and h6. (a) Kf5 results in the surprising mate g2-g4#. (b) Kh6 creates the kernel of a discovered check, with White’s knight on g5 now masking the c1 bishop’s path to the king. White takes advantage with Nxf7++, winning Black’s queen next move. As you know if you have read the chapter on discovered attacks, you want to pay careful attention whenever a king moves; chances for discoveries sometimes arise unexpectedly.