According to the facial feedback hypothesis, feedback from facial muscles can create or alter emotions. Testing this hypothesis has typically involved asking research participants to create facial expressions voluntarily, or by such involuntary means as holding a pencil in their mouths using their lips or their teeth (the latter requires the use of muscles involved in smiling). In this study, frowning or smiling expressions were involuntarily created using electrical stimulation and produced results consistent with the facial feedback hypothesis. The authors conclude as follows: “The finding that changes in felt emotion can be induced through brief and controlled activation of specific facial muscles….offers exciting opportunities for translational intervention.”