Unilateral contraction of facial muscles do effect emotions: a "failed replication's" failure to perform a replication.

Kop, Merckelbach and Muris (1991) reported a failure to replicate Schiff and Lamon's (1989) finding that unilateral muscle contractions induce emotions and influence cognitions in a manner which reflect those emotions. However, the procedures they used were different from the original experiment in substantive ways. These differences are described and it is explained how they account for the failure to replicate. This discussion helps illustrate the nature of the phenomenon which has been shown to be both robust and clinically relevant.