Laughter

 

"Laughter is a reflex, but unique in that it serves no apparent biological purpose; one might call it a luxury reflex. Its only function seems to be to provide relief from tension.
    "The[re] ... is a striking discrepancy between the nature of the stimulus and that of the response in humorous transactions.
    "When a blow beneath the kneecap causes an automatic upward kick, both 'stimulus' and 'response' function on the same primitive physiological level, without requiring the intervention of the higher mental functions. But that such a complex mental activity as reading a page of Thurber should cause a specific reflex contraction of the facial muscles is a lopsided phenomenon that has puzzled philosophers since Plato. ...
    "Humour is the only form of communication in which a stimulus on a high level of complexity produces a stereotyped, predictable response on the physiological reflex level. Thus the response can be used as an indicator for the presence of the elusive quality that is called humour—as the click of the Geiger counter is used to indicate the presence of radioactivity.
    "Such a procedure is not possible in any other form of art; and, since the step from the sublime to the ridiculous is reversible, the study of humour provides clues for the study of creativity in general."

~ Arthur Koestler, composite quote from his book Act of Creation and his entry on 'Humour' in Encyclopaedia Britannica —using "dense academia-speak" to say that humour has psychological benefits [Cartoons by Thurber. Hat tip Gordon McLauchlan's Acid Test]