Social norms define the story that can be told. It is alright to talk in public about nuclear disasters but not about our experience with sex techniques. We delight our client if we tell him that we are happy to see him, but it would be unwise to admit that we are in a hurry and have to move on to the next order.
Meanwhile it is quite easy to control our verbal output, our voice and our facial expression are difficult to restrain. Models such as the Facial Action Coding System (FACS) analyze facial expression by splitting it into action units related to facial muscles. This allows to identify emotions even though the speaker tries to hide them. Authentic facial expressions follow the rhythm of speech. They occur during or even before the speaker talks about his/her feelings. Fake expressions appear after speaking, they last longer and often end abruptly. (David J. Lieberman, Never Be Lied to Again)
Dan Hill describes in his book "Emotionomics" various examples of companies testing new products and advertising campaigns using facial coding. Dr. Paul Ekman, developer of FACS, offers on his website interactive training to improve the reading of micro-expressions. These facial expressions often occur, when people deliberately try to conceal their emotions (or unconsciously repress their emotions).