Black faces the threat of mate with RxR, so if he’s going to take the offensive elsewhere he will need to work with checks that force White to play defense. The checks he can give with his queen—Qxh2, Qf1, or moves to the g-file—don’t quite work; but how about 1. …Bxh2+? White’s only legal reply is 2. Kh1, retreating into the corner. But now the full kernel of a discovered check has been completed: Black’s queen is behind his bishop and aimed at White’s king. This almost enables a mating sequence with 2. …Bg3+ 3. Kg1, Qh2+ 3. Kf1, Qxf2#. That last move won’t succeed here because of White’s knight on d1, however, so Black needs something else for his bishop to do as it clears the h-file and discovers check. It can’t attack anything; it’s on a dark square and all of White’s pieces are all on light squares. But consider whether it usefully might block any lines. With 2. …Be5, Black severs the protection White’s queen had provided to the rook on e8. Again White must move his king to g1; and now Black plays RxR.