International audience Electromyographic techniques are used in a preliminary study of facial expression in macaque. The subject, a young adult male, is sitting in a primate chair. The muscular activity of the anterior belly of the digastricus, of the orbicularis oris, and of the muscles of the nape are recorded during yawns, threats and lip-smacking. The electromyograms are synchronized with photographies. The orbicularis oris is not active during threat, even if the teeth are fully exposed, but is active, although constant when the teeth are gradually completely exposed, during the last phase of mouth opening in the yawn. The exposure of the teeth, and especially the large canine of adult males, during the yawn, appeared to be merely linked to the widest opening of the mouth. This suggests, with other significative differences, a distinct communicative function between threats and yawns.