Body Language: Smiles
The history of research in the smiles field isn’t as laughable as the subject would suggest, French scientist Guillaume Duchenne de Boulogne used electrodiagnotics and electronic stimulation to distinguish the smile of real enjoyment and other kinds of smiling by experimenting with the heads of people who were executed in the guillotine testing how facial muscles reacted.He found out there is two sets of muscles that control the way we genuinely smile, zygomatic major muscles which run down the side of the face and connect to the corners of the mouth, and the orbicularis oculi muscles that pull back the eyes.The zygomatic majors pull the mouth back exposing the teeth and enlarging the cheeks, the orbicularis oculis however make the eyes narrower and cause wrinkles in the corners of them.
Keep in mind the zygomatic major muscles can be consciously controlled allowing people to show insincere friendliness or subordination through fake smiles, the orbicularis oculis however can’t be controlled acting independently when feeling pleassure and reveal our true feelings …if you want to know how to distinguish genuine enjoyment smiles, observe the wrinkles in the corner beside the eyes (in the side photo try to spot which is real and fake, I made it harder as the model has glasses 
), the eyebrows will also slightly dip down.Ever wonder why they ask you to say “Cheese” when taking a photo? pronouncing the word pulls back on your zygomatic muscles but they forget about the orbicularis oculis resulting in a fake smile.
