The two queens are faced off against each other. Each has protection from a rook. If any vulnerability exists in the enemy queen’s guard, it must be found. Again White has no way to go after the black rook on f8, but once more the practice of inspecting his checks pays off: he finds Rg3+. Black can't move his king to h8 because the square is attacked; and if he moves his king to f7, his queen becomes loose because its line to the rook has been severed. Black is better off with QxR, thus allowing h2xQ and the trade of his queen for a rook.

When a target is protected by another piece and the guardian is next to its king, consider this a possible vulnerability. A check may force the king to interrupt the target's protection and leave it loose.