An interesting and inexplicably unsettling test to see how well you can identify a fake smile. At the end it includes an interesting description of the differences. I got 16 out of 20 correct:
http://www.bbc.co.uk/science/humanbo...es/index.shtml
This is just one of a series of such tests, but I haven't had the few spare minutes to poke around the others yet:
http://www.bbc.co.uk/science/humanbo..._surveys.shtml