Once we had the idea that concealed feelings might be evidenced in these very brief micro expressions, we searched and found many more, typically covered in an instant by a smile. In a related essay on suicide faces, the Swiss psychologists Michael Heller and Veronique Haynal describe FACS experiments that reveal significant differences in facial expressions between suicidal and non-suicidal depressed patients. The two researchers interviewed residents of a Geneva psychiatry ward, half of whom had recently attempted to kill themselves. Other researchers have used FACS as a facial polygraph. According to several papers in the anthology, the telltale sign of a genuine smile isn't a wide grin but a deep eye scrunch.
Real smiles are also shorter and smoother in execution than anxious or faked varieties.
One can only imagine what HMOs could do with such a diagnostic tool. And yet FACS itself is hardly perfect. But while the face is a key signal system, there are others, like the voice and gestures, that may have more pivotal roles with certain emotions. And FACS may never be able to pinpoint exact patterns for emotions like jealousy or disappointment. Another barrier to progress is FACS's speed.