For me, non- verbal communication is the key to people's thoughts and emotions. This key is maybe underestimated because most of us think the most important factor in a conversation is verbal communication.
After reading my sheets and watching the video I realized maybe someone can say and promise lots of things that are actually not real,but that person would not be able to hide his emotions and his feelings and that's because people can't control non- verbal communication ( facial expressions, tone of voice, gestures, eye contact, etc. ) you can fake a smile but it would never be the same as a real one.
So I agree with  the saying "your actions speak louder than your words", you can tell the personality of a person  by HOW they express what they're saying no matter WHAT they're saying. For example, few days ago my english teacher told us how she finds out who's paying attetion to her, the only thing she has to do is watch her students faces, she can tell who is interested in the class by how we act, some of us just stare at the wall while others yawn, we are actually not saying anythig but she can tell how we feel. Another example is when a person you are talking to is always looking at the floor, that can mean that is shy; we can also take as an example they way how best friends or couples communicate with eye contact, when you look at a really close friend you can asume what that person is triying to say without using words.
In conclusion,by watching people's non- verbal communication, sometimes we can tell how a person feels or thinks, by relying on gestures and facial expressions people say more things than with words.