It is often said that our facial expressions are the mirror of our moods, but recent research says this is not so. For example, it was thought that an expression of fear was universal, but the inhabitants of Papua Guinea, when are shown a photo of a face which for ‘Westerners’ shows fear, instead see a threatening and aggressive expression. It is believed that our facial expressions are tools to guide social relationships. A smile, rather than an exhibition of good mood or happiness would be a message that says “go on as you are doing”. Instead an expression of disgust, as a reaction to what has just been said, says “please change the subject”. The evolutionary usefulness of all this is to send info that helps someone take the next step. Instead, to let people know how we feel deep down is not wise and may even be dangerous. The fact that our facial expressions are not innate but instead learned and a reflection of the culture of the place has practical implications. For example, Artificial Intelligence instruments are being developed to analyze, live, the facial expressions of masses of people (as in airports), in the hope of identifying those who have bad intentions. Naturally a frightened face must not be confused with a threatening one. In some cases, matters get complicated. For example, laughing at the wrong moment could signal we want to be ironic or even hostile and not that there is something funny. Children’s faces are very expressive from a very young age and long before they learn to speak. The aim is not so much to know how they are, but rather to get info on what we can do to help them. Replying with a facial expression means using a powerful means of communication before you learn to speak.