http://www.bbc.co.uk/science/humanbo...es/index.shtml
You get 20 miniscule movies of people of different ages, race, gender etc. who begin to smile. You have to ascertain which of them are faking it and who are genuine. It is a good exercise if you have a little time to spare. It is based on the research of a certain Prof. Paul Eckman (does HL2 ring a bell ?).
I got 8 out of 20 correct. I'm not that good with people.
Try it out.