We all know that we communicate a great deal with our faces. We show a broad range of emotions. We read each others facial expressions to pick up on nuances, to detect whether what we are hearing from the other person is really what they are feeling. Everyone knows at least one person who has a great poker face and can hide their emotions and not show much through their facial expressions. I can think of card players, negotiators, enforcement, military and other professions who work at not showing emotions through facial expressions. The chapter in this book says that people who are trained to look for deceptions and people who are naturally good at reading people's faces, read the whole face, including the eyes. It is possible to tell if a person is using a false smile because a person using a false smile just uses muscles in the lower face which only affects the shape of the mouth. A true smile involves muscles higher up in the face and are in a sense 'cheek pullers'. The eyes are narrowed in a true smile while a false smile only turns up the corner of the eyes.
Dogs are more limited in the range of using their lower facial muscles and don't use their mouths or facial expressions to tell lies. Their muzzle is also constructed differently than our mouth and thereby has limited restrictions on the possible number of expressions. This book points out that almost all vertebrate animals, except humans, have a muzzle. For example, cats, dogs, cows, pigs, alligators, bears and deer all have a projecting mouth which forms their muzzle. Their muzzle is a basic survival tool as they have to be able to grab, gnaw, nip or seize food. We don't need a muzzle as we have hands which we use to bring food directly to our mouth. Who would have thought this???
A dog's mouth does give information about anger, dominance, aggression, fear, attention, interest or relaxation. The chapter on facial expression describes in length reading mouth shape including how the tongue hangs, the way teeth are shown and associated head positions. I know I will never remember all of the different dog expressions and what they mean especially when I am out with my dog on a walk and we meet other dogs. It is an art to read people's facial and body expressions, reading dogs requires even more expertise. For now I will rely on the wagging tail, the position of my dog's ears and whether his hackles are up. I must go now and read my dog's face while he is lounging in his lazy boy chair.