> The key to faking a real smile is in wrinkling the eyes.
The wrinkling is not a very reliable indicator of fake smiles [1]. A real smile does indeed involve muscles around the eyes, but wrinkling could be caused by the cheek muscles pushing upward too.
Some more indicators of a real smile are, IIRC
- curling corners of the mouth
- corners of the eye pushing inward
- short duration
- it starts and ends smoothly
- symmetry
[1] Source: Having recently read "Telling Lies" by Paul Ekman (and that was a HN recommendation too)
There are 20 short clips of people smiling. Can you spot which ones are fake and which ones are genuine? (The test takes about 10 mins)
http://www.bbc.co.uk/science/humanbody/mind/surveys/smiles/