This time it's Black who sees that White has left his king and queen adjacent on a diagonal. He looks for a pinning tool and finds it in the dark-squared bishop, which he can play to g5. What will White do? He might play QxB, but his more immediate defense is the same as in the previous position: f2-f4, interposing a pawn and disturbing the pin. Black follows the continuation in his mind—Bxf4, then White plays QxB. It looks bad, but before writing off the idea consider the consequences of White’s feared move. Ask in particular what pieces Black can direct at White’s king, and with what result, once the queen leaves its station. Here the answer is that Black has a battery of queen and rook on the b-file. It’s another case like the one a moment ago where your queen can land near the enemy king, and with protection; and it’s another case where the move results in mate, this time on the spot with Qxb2. So again the pin of the queen (this time with Bg5) works fine despite the fact that the pinning piece has no defenders.
The general lesson of these positions resembles a point from the section on knight forks: if you have a pin (or fork), but it looks unplayable because the piece you would use to execute it can be taken, ask what the consequences of such a capture would be and especially what checks would then become possible for you. A potential fork or pin is a type of forcing move that often costs your opponent material if he doesn’t capture the piece making the threat. Forcing him to make that capture means you're controlling the movement of the pieces on the board, which in turn is the key to creating tactical strikes of all sorts. From time to time a failed pin can be better that a successful one, as this position shows.