This is a neat little tactic from Game 28 in Logical Chess Move by Move.
It reminded me of the last tactic I worked on last night at ChessTempo. I must have spent about 20 minutes trying to figure out how to mate or capture the queen. I kept going over the same three 'trees' over and over again thinking I was overlooking something.
It failed to occur to me to consider the tactic was directed at the rook instead of the queen or king. The lesson learned (or 'learnt' for you Brits) was keep moving down the totem pole of targets (king, queen, rook, etc.) until you find the proper tactic.
In the tactic presented here, it is fairly obvious checkmate isn't on the horizon and the queen is off the board. The one little guy sticking out is that pawn on a7. I would have considered taking the pawn, but probably would have been at a loss as to how to extract my knight after said capture. And therein lies the neatness of this tactic.