The ability to mimic genuine emotions regardless of the lack of relative emotional experience is unique to psychopaths, and it serves to gain trust from people so they may manipulate and deceive them. Relevant research has theorized that psychopaths possess selective affective traits, particularly they display a lack of empathy, remorse, and an overall limited range in emotions.
Book et al (2015) studied individuals with higher scores on psychopathy to determine if they could create fearful facial expressions, and if they could appear genuine to others while faking expressions of remorse. The overall findings of these three studies indicate that psychopaths are able to imitate and express genuine emotions as a way to be perceived as normal by others and deter being detected. These outcomes not only provide insight about psychopathic traits, but also about the distinction between feeling and expressing an emotion. In other words, the expression of an emotion can be learned and communicated to others, even if the emotion itself isn’t subjectively experienced by the psychopathic individual.
http://link.springer.com/article/10.1007/s40806-015-0012-x