"The surface of the psychopath... shows up as equal to or better than normal and gives no hint at all of a disorder within. Nothing about him suggests oddness, inadequacy, or moral frailty," psychiatrist Hervey M. Cleckley wrote in his 1941 seminal work, "The Mask of Sanity," according to PsyPost.

Psychopathy is a personality disorder characterized by manipulative behavior, a lack of empathy, fear and remorse. However, new psychology research suggests that while psychopathic individuals don't feel these emotions as strongly as others do, they do a better job of pretending than the average person.

Angela Book of Brock University in Canada and a team of researchers conducted three experiments on prison inmates and students to examine the ability of psychopathic individuals to mimic normal human emotions. They discovered "that individuals with psychopathic traits may be able to express fraudulent emotions that appear genuine to the people around them."

"Psychopaths tend to lack fear and we know they lack remorse," said Book, according to The Brock News. "We wanted to know if they were better able to fake these things."

Book and her team conducted three experiments to determine how well prison inmates were able to mimic facial expressions that indicated concern and empathy.

"It's difficult to spot a psychopath; in fact, they can look actually like they're more genuine than other people," Book said, according to The Brock News. "Part of it is that most people don't have to fake emotions all the time, so they don't have any practice at it. But someone who doesn't feel these emotions will have practice at faking them, so they will probably be better at it."

Book and her team - funded by a grant from the Social Sciences and Humanities Research Council - found that results from their experiments were consistent with the mimicry theory, first put forth by UBC researcher Daniel Jones in 2014. 

The team's results are reported in their study "The Mask of Sanity Revisited: Psychopathic Traits and Affective Mimicry," published in the online journal Evolutionary Psychological Science.