A color scan suggests an almost-fork for Black with Nxf3. If only White's king could be moved to h2! Well, but there is a resource you can experiment with for that purpose: Rxh2+. How would White respond? If he moves the king to f1 or g1, examine the resulting position: he loses his d2 rook to RxR (a skewer). So presumably he will instead play KxR. Examine the resulting board. Black’s knight will be on the dark square where it already sits; White’s rook and king will be on d2 and h2, respectively. So Black then forks them with Nxf3+ and gets back the rook (as well as the two pawns captured along the way).