FAKE LAUGHTER always looks fake
KEY CONCEPT : Uproarious laughter is expressed with an open mouth, actively squeezed cheeks, clenched eyelids (including tears, for some) and spontaneous, infectious sounds.
A real laugh erupts with a burst of emotional energy, a sudden increase in a person's arousal level which they relieve by a sharp release of air through an open, smiling mouth. As shown in Figure 1, real laughter is much more spontaneous and uncontrollable than a typical smile, and it is both pleasant to experience and hear.
Alternatively, fake laughter is a common feature of stock photos, like beer ads, where models, who are not trained actors, unsuccessfully pretend to laugh uproariously on demand. As shown in Figure 2, the models are faking it, and you know it.
Eyes Squeezed Tight
Fake laughs always lack the eye squeeze – that’s what makes them look fake. The combination of a gaping, smiling mouth and staring, open eyes is one of the most off-putting expressions in the expressive palette of the face. Since there is no bona fide expression which is remotely similar, people who are posing a fake laugh look ridiculous rather than amused, like they are attempting to catch flies with their widened mouths. There is, in fact, a range of action in the true laugh; the more robust the expression, the wider the mouth and the more tightly compressed the eyes. But even less intense laughter features closed eyes; just like the cough or the sneeze.
Figure 3. Stylized faces, when done well, give us the key features of an expression with no extra, distracting detail. Here an unknown artist puts down all the key elements of the Real Laugh. The eyes are closed and narrowed; there is a little crescent-shaped fold under the eye; the cheeks are full, bounded from below by a deep naso-labial fold; the mouth is widened side-to-side and top-to-bottom, and there are dark pits at the mouth corner, where the teeth curve into the face. Pretty good for a cartoon!