This position doesn't involve a mating threat but it depends on a similar train of thought. See the kernel of a discovery on the third rank: the White rook, White knight, and Black queen in a line should be suggestive. What threat can the knight make as it evacuates e3? Black’s king is out of range—on this move. But look for moves that would allow the knight to give check a move later, and consider whether that check might be of interest—if not as a mating threat, then as part of a double attack. Black’s king and rook are poised to be forked from h6. Ng4 thus threatens Nh6+. Black has the choice of replying to Ng4 by (a) taking the knight with the h5 pawn, losing his queen to RxQ, and then taking White’s rook with the pawn that would then be on g4; or (b) he can save the queen and lose the exchange to the coming knight fork. Either way White takes a decisive advantage.

This position resembles the mating threats we have been considering lately because in either case the unmasking knight doesn't check or capture as it unveils the discovered attack; rather, it moves into position to threaten a crushing blow a move later.