Ancient Greek philosopher Aristotle viewed laughter as “a bodily exercise precious to health.” But like some claims to the contrary, laughing probably has little influence on physical fitness. Laughter does【C1】_____short-term changes in the function of the heart and its blood vessels,【C2】__heart rate and oxygen consumption. But because hard laughter is difficult to【C3】__, a good laugh is unlikely to have【C4】_____benefits the way, say, walking or jogging does.

【C5】_____, instead of straining muscles to build them, as exercise does, laughter apparently accomplishes the opposite, studies dating back to the 1930’s indicate that laughter 【C6】_____muscles, decreasing muscle tone for up to 45 minutes after the laugh dies down.

Such bodily reaction might conceivably help【C7】_____the effects of psychological stress. Anyway, the act of laughing probably does produce other types of【C8】__feedback that improve an individual’s emotional state.【C9】__one classical theory of emotion, our feelings are partially rooted in physical reactions. It was argued at the end of the 19th century that humans do not cry【C10】_____they are sad but they become sad when the tears begin to flow.

Although sadness also【C11】_____tears, evidence suggests that emotions can flow【C12】__muscular responses. In an experiment published in 1988, social psychologist Fritz Strack of the University of Wurzburg in Germany asked volunteers to hold a pen either with their teeth-thereby creating an artificial smile — or with their lips, which would produce a(n)【C13】__expression. Those forced to exercise their smiling muscles【C14】__more exuberantly to funny cartons than did those whose mouths were contracted in a frown, suggesting that expressions may influence emotions rather than just the other way around.【C15】_____. the physical act of laughter could improve mood.

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