The smile, a facial expression traditionally used to convey joy, pleasure, or amusement, is now mainly used to suppress rage, according to a five-year study released Monday by the Countenance Institute. 'More than 85 percent of smiles are involuntary responses to mounting anger,' the study read in part. 'In addition, the length and intensity of these smiles directly correspond to the amount of anger the smile is concealing. A smile that lasts less than two seconds represents just a passing annoyance, while a smile of four to eight seconds indicates a genuine hatred for its target.' The study noted that individuals smiling for more than one minute while nodding and baring their teeth are most likely preparing to kill the person they are smiling at. 