" Feedback smile. Smiling itself produces a weak feeling of happiness. The facial feedback hypothesis proposes that ". . . involuntary facial movements provide sufficient peripheral information to drive emotional experience" (Bernstein et al. 2000). According to Davis and Palladino (2000), ". . . feedback from facial expression [e.g., smiling or frowning] affects emotional expression and behavior." In one study, e.g., participants were instructed to hold a pencil in their mouths, either between their lips or between their teeth. The latter, who were able to smile, rated cartoons funnier than did the former, who could not smile (Davis and Palladino 2000). "

― David B. Givens , The NONVERBAL DICTIONARY of gestures, signs and body language cues