It is really a hot and big topic to explain. It is related to the so-called micro-expression study. I once saw a serial soap drama named lie to me, which is focusing on how micro-expressions help the star to crack tough case he met. The micro-expression will only last for about a fifth of a second, hard to catch. It is a natural and instinctive reaction to what people heard and saw. If the expression on people's face, it might be fake. If someone is lying, you can see the expression on his/her face means different to what he/she is saying. When someone is preparing to lie, he/she usually look directly at other's eyes to convince the people who are listening to him/her. Yet, as I said, it is a big topic. If you are really interested in it, I suggest you to buy some books on this topic, which could help you learn more.