The analysis here sounds almost the same as in the previous frame. Start by looking for the ingredients of a double attack and work backwards. If you ask whether White has any loose pieces, the answer again is “not quite"—but the b2 rook is attacked once and protected once, and by another White piece (the queen) rather than a pawn. This means the rook is underdefended; if Black can attack the rook and give check, the rook will be lost. But all this presupposes that Black can get his queen onto a square where it can check White's king and attack the b2 rook at the same time—i.e., d4. Only Black’s own knight already on d4 stands in the way. The trick is to vacate the square in a threatening way that requires a time-consuming response from White; so you look for captures and threats the knight can make. Nxf3+ forks White's king and rook and requires the reply g2xN. Qd4+ then wins the rook at b2 as described above.

A general point to take away from this position and the previous one is that when you examine your opponent’s pieces, you want to note not just whether they’re protected but how they’re protected and whether they also are under attack from other directions already. It's worth studying these two cases until it's clear that the targets (the rook on b2 here, and the bishop on h6 in the previous position) are vulnerable to forks in the same general way that loose enemy pieces would be.