Which of the pairs below fails the classification that the other three obey?

Three of the pairs join a piece of clothing to the part of the body it is worn on — the cap on the head, the glove on the hand and the sock on the foot. The odd pair gives the stuff the garment is made of instead; the body part for a scarf would have been the neck. It reads smoothly because wool and scarves belong together in the mind, but the group is built on where a garment is worn.