Black’s bishop is aimed at White’s king with the usual pawn in the way. If White’s queen were on d2 or f2 rather than e3, Black would have a classic discovered check with a threat against White’s queen. Meanwhile Black also has two other pieces—his rook and queen—trained on the White king's territory. How to exploit all this? Use one threat to improve the other. More specificially, try the same logic seen in the previous frame, in which you draw the queen onto the square where you want it by putting one of your own pieces there.

Thus suppose Black plays Rf2. What does this threaten? Consider the best checks Black would then have; he could play Qg2# or Qxh2#. After Black starts with Rf2, White can fend off that threat of Qg2# by playing Rg1; now g2 is defended. But that doesn't help with the threat of Qxh2#. The only way for White to deal with that threat as well as the threat of Qg2# is by responding to Rf2 with QxRf2. That does take care of both mating threats—but now Black's discovered check e4-e3 wins the queen for a rook.