A person's can hide many things and it is difficult to figure out what he/she is actually thinking. A body language expert based in Atlanta, Patti Wood, MA explains, "There is a smile called the 'Duping' smile or 'Dupper's Delight' which is typically a little smile that comes across the face when a liar or deal-maker or cheating-winner thinks they have duped someone."
You want to put people at ease
There are countless reasons behind a smile. Many people have a naturally smiley face. And, if someone wants to become a smooth socializer, your smile can help you. Psychology Today pinpoints,"We automatically copy the facial expressions of others. We reciprocate and in social groups it can be contagious. People respond to, and evaluate, those who smile differently and more positively than those who do not."
You're hiding how you really feel
Many people cover their emotions behind smile. As Jonathan Gratch, based at USC's  Institute for Creative Technologies in Playa Vista, California says,"The nature of a smile also communicates subtle information about its authenticity." He further said, "A smile that starts and ends too quickly is seen as not genuine."
You're under pressure
People often smile when in trouble or at unease. A family and marriage therapist in Philadelphia, Shadeen Francis,"A common example of this is laughing when you receive bad news, freezing when you are in danger, or making jokes when you are uncomfortable." The therapist further added,"These incongruous responses are just a few of the brain's many ways of managing overwhelming emotional circumstances. An unexplainable smile may also be a signal of distress, especially when others are around."
