This position introduces a new type of kernel to absorb: the knight in front of a heavy piece (a queen or rook) on the same file. If White's knight can vacate its square with a check, White’s queen will be able to take Black’s queen, which is loose. White thus plays Nxf6+—a fork of Black’s king and queen. Black has to fend off the check with g7xN; and now the game effectively ends with QxQ+.
If Black instead replies to Nxf6+ with Kf8, then it might seem that White would simply play NxQ, but he can do better: Qxe8#. Notice, too, that with Nxf6 the knight seals off h7 as a flight square. Or suppose Black replies to Nxf6+ with Kf7. Now White again takes Black's queen, but uses the knight on f6 to do it. Capturing with the queen allows Black to reply KxNf6.