听力原文： When a child injuries himself the American parent's usual response is to kiss the child's injury. This parental habit is also observed in many other cultures. This practice may be a survivor of the primitive custom of 'sucking out evil'. At primitive times, a healer traditionally withdrew, by using his mouth, infection from the afflicted part of a patient's body. In fact, except in those cases where the patient is bitten by a fatal snake and the actual poison will be sucked out, there is no obvious curative effect to be derived from the sucking. Then the common parental habit of kissing a child's injury to make it go away seems to be purely psychological. The psychological effect is also not negligible. When a patient believes in a cure, there is a much greater chance that it will work, even when the cure is medically groundless. Thus kissing a child's injury to make it better can always ease the child's pain and give him the mental confidence that will hasten the body's own healing process. What do American parents usually do when their child injuries himself?