Study reveals laughter really is the best medicine

http://www.bbc.co.uk/news/science-environment-14889165

"People feel less pain after a good laugh ... Tittering and giggling did not elicit any physiological effect; only a good guffaw did the job ... This theory creates the scenario of our ancestors sharing laughter around the fire, possibly the emergence of the first clowns, clubbing each other for comic effect"