Jokes are funnier if the audience already is smiling was a theory expounded by the 18th century naturalist Charles Darwin, and a modern researcher confirmed the idea.

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Social psychologist Fritz Strack reportedly proved recently that even a "smile" force by holding a pen in the teeth with the lips pulled back significantly, increased the humor "smilers" saw in a series of cartoons.Darwin claimed more than a centuary ago that facial expressions could intensify emotions rather than just mirroring them, and that people really could be happier if they forced themselves to smile.

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