Duchenne

Duchenne Smiles, from Wikipedia "Smile" Entry:
Researchers have identified a number of different types of smiles.

* The "Duchenne smile", after the researcher Guillaume Duchenne, is the most studied, and involves the movement of both the zygomaticus major muscle near the mouth and the orbicularis oculi muscle near the eyes. An example of the smile is shown in the girl's smile at the top of the page. It is believed that the Duchenne smile is only produced as an involuntary response to genuine emotion, and is therefore what one could call the "genuine" smile. Due to the involvement of the muscle near the eyes, it is sometime said that one can tell whether or not a smile is "real" by whether or not it "reaches the eyes".
* The "Pan American smile", on the other hand, is the voluntary smile involving only the zygomaticus major muscle to show politeness; for example, by a flight attendant on the former airline of the same name. Considered "insincere", this type of smile has also been called the "Professional Smile" by David Foster Wallace in his comedic short story A Supposedly Fun Thing I'll Never Do Again.