The authors report 3 experiments that examine a new mechanism by which overt head movements can affect attitude change. In each experiment, participants were induced to either nod or to shake their heads while listening to a persuasive message. When the message arguments were strong, nodding produced more persuasion than shaking. When the arguments were weak, the reverse occurred. These effects were most pronounced when elaboration was high. These findings are consistent with the "self-validation" hypothesis that postulates that head movements either enhance (nodding) or undermine (shaking) confidence in one's thoughts about the message. In a 4th experiment, the authors extended this result to another overt behavior (writing with the dominant or nondominant hand) and a different attitude domain (self-esteem).