] This experiment is designed to test whether you can spot
] the difference between a fake smile and a real one
]
] It has 20 questions and should take you 10 minutes
]
] It is based on research by Professor Paul Ekman, a
] psychologist at the University of California

Personally, I suck at this kind of thing... I need more context than just a face. But I still found it interesting, especially the discussion at the end.

BBCi - Science - Human Body - Spot The Fake Smile