Researchers from the University of Wisconsin-Madison have found there are three distinct varieties of smile - affiliation, dominance, reward - and people use different facial muscle combinations to forge them. The findings could help individuals influence the outcome of games and negotiations, and even assist facial reconstruction surgeons. The team cracked the smile code by gathering participants to review thousands of computer-generated expressions created using random combinations of facial muscles, although each one included some action from the zygomaticus (the facial muscle below the cheekbone that pulls the corners of the mouth into a grin, oft dubbed the "smile muscle"). ​Subjects were then asked for their perception of the smile - did it denote reward or dominance, was it affiliative, or was it not a smile at all? Once sorted, the smiles were then shown to two further sets of observers, allowing the researchers to determine the muscular recipe behind each kind of grin. The