The same idea in a different visual setting. White's knight on f4 masks his queen, which is aimed at the Black knight on h6. Black's knight is protected and thus is an unsuitable target, but since it's next to Black's king a substitution is possible: RxN+, inviting the recapture KxR. Now White is ready to play Nxd5+, and—after the king moves—NxQ. Notice that 2. Ng6+ also would work for White, since the knight would have protection on g6 from the rook on g1. But then White wins one less pawn.