Have you ever thought about why photographers ask their subjects to say ‘cheese’? A part of the answer might come from physiology and the work of the French scientist, Guillaume Duchenne de Boulogne back in the early part of the 19th century. For us, the authors, his empirical procedure was one of the great ironies in scientific research, for he used arguably the most despairing never-a-reason-to-smile people on earth to carry out the first ever investigations into smiling. He analyzed the chopped off heads of people executed by guillotine to study how the face muscles worked in distinguishing between smiles of true enjoyment and other kinds of smiling (That’s why genuine smiles are called the ‘Duchenne Smile.’) (Photo 18). Pulling facial muscles from a variety of angles to document which muscles corresponded to which smiles, Duchenne learned that smiles are controlled by two pairs of muscles. The first pair consist of the zygomatic major muscles, which trail down the side of the face and attach to the corners of the mouth and the orbicularis oculi, which pull the eyes back. The second pair are composed of the zygomatic major muscles that pull the mouth back, reveal the teeth and expand the cheeks and the orbicularis oculi, which cause the eyes to narrow in ‘crow’s feet.’ Why is all this physiology important to know? Because the zygomatic majors are consciously controlled, making them the primary mechanism in producing fake smiles (Photo 19). The orbicularis oculi, on the other hand, perform autonomously and expose our true feelings in a genuine smile. So the first place to assess the sincerity of a smile is to look for wrinkle lines beside the eyes. When people feel happy, signals awaken the portion of the brain that processes emotion, making the mouth muscles flex, the cheeks rise, the eyes crinkle up and the eyebrows dip slightly.