*The truth is written all over our faces.

I think that microexpressions are the single most interesting thing on the planet. I am beyond fascinated with them. Paul Ekman is by far one of the most important and well known psychologists to study and work with microexpressions. He started researching back in 1954 and hasn't stopped since. He is constantly working on new research or traveling the world teaching people what he knows. A microexpression is an involuntary facial expression or movement lasting only 1/25 of a second. A person can never really tell a lie, because their facial expressions (microexpressions) will always give it away. They cannot be controlled. A microexpression will always be backed by some sort of emotion even if the person expressing it does not realize it. Many times they can be difficult to pinpoint simply because of the fact that they happen so quickly. You have to know exactly what you are looking for. If someone is reading someones face/microexpressions the first thing they have to do is establish a base line. They will usually ask questions that they already know the answer to, which allows them to later determine if someone is lying.
My favorite TV show is called Lie to Me. It is based on Paul Ekman and his work with microexpressions.
I found a clip explaining a little bit about the show and the microexpressions. The Truth Is In Our Faces

I also found a picture from the show that points out some of the different microexpressions for each emotion we experience.