Final answer:
A Duchenne smile is genuine and includes the contraction of the muscles around the eyes, whereas a voluntary smile involves the muscles around the mouth. Duchenne smiles engage the orbicularis oculi, often displaying 'crow's feet' and can induce true happiness through the facial feedback hypothesis.
Step-by-step explanation:
A voluntary smile often only involves the muscles around the mouth and may appear as a simple curving of the lips. In contrast, a Duchenne smile, which is a spontaneous and genuine smile, includes not only the contraction of the muscles around the mouth but also the engagement of the muscles around the eyes, specifically the orbicularis oculi. This creates the characteristic 'crow's feet' around the eyes, signaling a true smile.
Importantly, a voluntary smile does not necessarily include a parting of the lips to reveal the teeth, nor does a Duchenne smile involve clenched teeth. The distinction between the two types of smiles suggests that a Duchenne smile is a full expression of happiness which can also induce a corresponding emotional state due to the facial feedback hypothesis, whereas a voluntary smile may not have the same effect.