Figure 51: À droite, contraction partielle de l'élévateur commun de l'aile du nez et de la lèvre supérieure: mécontentement, mauvaise humeur; à gauche, repos

This photograph is part of the first systematic exploration of the physiology of human facial expression. In order to demonstrate how each individual muscle contributed to creating an expression, Duchenne stimulated one or more muscles on one side of the face and left the other at rest.