Ancient Greek philosopher Aristotle viewed laughter as “a bodily exercise precious to health.” But _____（1） some claims to the contrary, laughing probably has little influence on physical fitness. Laughter does _____（2）short- term changes in the function of the heart and its blood vessels, _____（3）heart rate and oxygen consumption. But because hard laughter is difficult to _____（4）, a good laugh is unlikely to have _____（5）benefits the way, say, walking or jogging does.
_____（6）, instead of straining muscles to build them, as exercise does, laughter apparently accomplishes the _____（7）. Studies dating back to the 1930s indicate that laughter _____（8） muscles,decreasing muscle tone for up to 45 minutes after the laugh dies down.
Such bodily reaction might conceivably help _____（9）the effects of psychological stress. Anyway, the act of laughing probably does produce other types of _____（10）feedback, that improve an individual’s emotional state. _____（11）one classical theory of emotion, our feelings are partially rooted _____（12）physical reactions. It was argued at the end of the 19th century that humans do not cry _____（13）they are sad but that they become sad when the tears begin to flow.
Although sadness also _____（14）tears,evidence suggests that emotions can flow _____（15）muscular responses. In an experiment published in 1988, social psychologist Fritz Strack of the University of Wurzburg in Germany asked volunteers to _____（16）a pen either with their teeth-thereby creating an artificial smile-or with their lips, which would produce a(n) _____（17）expression. Those forced to exercise their smiling muscles _____（18）more enthusiastically to funny cartoons than did those whose mouths were contracted in a frown, _____（19）that expressions may influence emotions rather than just the other way around._____（20）, the physical act of laughter could improve mood.