Figure 2.4.2.4[White to move]

White has no checks with his rook, but you want to be equally alert for attacks you can make against loose pieces. Here the bishop at h5 is Black's only loose piece, and the rook can attack it with Rf5. From that square you see the rook also can attack the knight at e5. The knight is protected by the Black queen—but it also is already attacked by the White queen. So the knight is a classic case of a piece that is threatened once and protected once and therefore is as good as loose. If Black moves the bishop after White plays Rf5, White then plays RxN and Black dares not recapture lest he lose his queen to QxQ. White wins a piece.