People with high levels of psychopathic personality traits may move their heads less when they’re talking than those with lower degrees of psychopathy, new research has revealed. According to the study authors, this subtle pattern of nonverbal communication had previously been identified in male psychopaths, and their findings suggest that the same tendencies also apply to women.

Psychopathy is characterized by a constellation of affective deficits such as callousness and a lack of remorse, as well as dysfunctional behaviors like pathological lying and manipulation. Excessive impulsivity and irresponsibility are also frequently demonstrated by individuals who fit the label, although it can sometimes be difficult to spot a psychopath due to their ability to hide these antisocial characteristics.

However, prior work has identified a number of surprising tell-tale signs in the body language of psychopaths. For example, men with high levels of psychopathy tend to use more hand gestures than those with lower scores, while short bursts of blinking have also been linked to the condition.

Reduced head movement during interviews has been identified as yet another potential give-away for psychopathic men, although very little research has been conducted on women. To fill this void, the study authors filmed clinical interviews with 213 incarcerated women, during which they administered a psychopathy questionnaire in order to assess the degree to which each participant meets the criteria for this diagnosis.

An automated detection algorithm was then used to monitor each woman’s head movement in every frame of video. Overall, the researchers found that women with higher psychopathy scores tended to keep their heads more still than those with lower scores.

On average, participants spent 40 percent of the interview with their head within the “range of moderate movement” away from its average position. However, psychopathic women kept their head within a “range of minimal movement” away from its average position for the majority of the interview.

Spending more time with one’s head within this minimal movement range was positively correlated with psychopathy scores, while time spent in the moderate range was negatively associated with the condition.

Based on this observation, the study authors state that their results “help identify a unique pattern of head dynamics characteristic of women scoring high on psychopathy, specifically, exhibiting more stationary head positioning during clinical interview administration.”

Noting that it can often be difficult to spot a psychopath using behavior alone, the researchers go on to explain that keeping an eye out for nonverbal cues may be “of particular importance when studying a constellation of behaviors that are inherently deceptive.”

The study has been published in the journal Personality and Individual differences.