A classic route to the smothered mate arises when you make a sacrifice on a square next to the enemy king; the sacrifice requires your opponent to recapture there with a different piece and seal his king onto its square. Thus in the diagrammed position Black plays Qg1+. Since the queen has protection from its bishop on a7, White can’t capture with his king; he is forced to play RxQ. But now his king is trapped and is easy prey: Nf2#.