The important thing is to see not just how a mate looks when it is finished but how it can look when it is a move or two away. The tipoff here is the absence of Black’s f-pawn. Anytime a pawn in front of the king is absent (either because it has advanced, changed files, or left the board entirely) think about ways to take advantage. The classic way to exploit a missing f-pawn is to get a bishop or queen aimed down the diagonal toward g8, and then to add pressure against h8—with a heavy piece or with a knight. Here White has a knight available for the task. He sees that Greco’s old fashioned mate can't be created because he would have to sacrifice his rook to open the h-file and then would have no heavy piece left to put there. But his rook does pin the h7 pawn, which means White can land his knight on g6; and his bishop has a clear path to the diagonal with Bc4. So White works with checks: 1. Ng6+, Kg8; 2. Bc4#.