Figure[Black to move]

Do you see the geometry of a skewer for Black? Look for two White pieces on a line that one of your pieces can reach with an attack; see that on the first rank White has a queen and rook. Black can put a rook on c1, skewering them with protection from the queen on e3. But since this would be a case of a rook taking a rook (after White’s queen moves), it only works if the targeted rook is loose, which it isn’t. Or is it? It has protection from White’s king; then again, it also is attacked already by Black’s queen, so White’s king wouldn’t be able to recapture. Black thus should play Rc1 after all. When White moves his queen, the coast is clear for RxR or QxR+.

There is a little more to say about that last choice. Which is better? QxR+: it's a check, and so keeps Black in control. To illustrate the point, suppose White replies to Black’s initial Rc1 with Qh5. Now if Black plays RxR, White has Qe8—mate! Whereas playing with checks wins Black the game: after White’s Qh5 is 2. …QxR+; 3. Kg3, Rc3+ (another check to protect against the aforementioned mate threat); 4. Kh4, Qf2+ (still another check); 5. Kg5, Rg3+, and with careful play Black has an eventual forced mate as the White king is driven into treacherous territory infested with Black pawns. Assuming White sees all this, he will respond to Rc1 in the first place not with 2. Qh5 but with 2. QxR, BxQ, accepting the loss of a queen for a rook.