Black has the kernel of a discovery on the d-file: the bishop is poised to give check with Bxh2 and unmask an attack by the rook at the same time. But an attack against what? The only target on the d-file is White’s pawn, which anyway is protected. Again, in this situation consider whether you can take the bad target with one of your other pieces, and so cause it to be replaced by a valuable one. Here Black can take the pawn with his bishop, which after Bxd3 threatens both White’s queen and his rook on f1. White has to play QxB if he wants to avoid losing the exchange to BxR—but after QxB, the board is arranged for the discovered attack Bxh2, sacrificing a second bishop to win the queen.