White looks for a promising geometric pattern and sees that Black has two pieces—the bishop and knight—on the same rank and separated by one square: the classic setup for a pawn fork. The only hitch is that the bishop is an unsuitable target because it can capture the pawn. White asks whether he can take the bishop with another piece, causing it to be replaced by a better target; he can, with NxB. Black recaptures with RxN, and now White plays the fork f2-f4, winning the knight after the rook moves.