Bxc6 is such a strong defence in the diagram, freeing c5 for
the king, that Bb6 must be prepared to cope with it. This leads to a
duel between the white queen and black bishop for control of e5.
1.Qh2 (threat 2.Bb6) Bf4 2.Qxh5 Bg5 3.Qh8 Bf6 and now 4.Qxe8 threatens
5.Qd7 and the bishop finds that it must block the square it has been
trying to prevent White from guarding 4...Bxe5 5.Bb6. The b2 knight can
only delay the mate by capturing on d3, or play 4...Sc4 5.Rxc4.