Black’s king and queen are adjacent; and sometimes when this is so, a check or two can arrange the pieces for an easy removal of the guard. So White experiments with checks and finds Qxb4+. The challenge for Black now is to move his king without then losing his queen to a skewer. His first thought might be Ke3, permitting the king to keep guarding the queen; if so, White uses our now-standard technique for removing a king as a defender: he throws another check at it with Rc3+. The king can't move up; it can only move down to e2, leaving the Black queen loose and doomed. The same basic result follows if Black instead replies to Qxb4+ by moving his king up to e5: White adds another check (Rc5+) and drives off the king, permitting QxQ next move. Finally, suppose Black responds to White’s Qxb4+ with Kf5. Now White sees a classic opening for a flush check with Rf6+, drawing the king away from the queen by calling for KxR and thus permitting White to play QxQ+ on his next move (and QxN a move later).