Psychopaths, by definition, have a hard time understanding why the rest of us have so many pesky feelings. And it appears this lack of empathy extends to one of the most natural (and least resistible) of states: yawning. In a new pilot study, published online in the journal Individual and Personality Differences, researchers had 135 undergraduates complete a questionnaire that assessed participants' levels of psychopathic traits. Then, participants watched three videos in a random order — one was of a person laughing, one had someone with a neutral face, and one showed a person yawning. The researchers closely monitored participants' faces, including looking for minute facial muscle activity. Related: What To Say In Life's Most Difficult Situations Results showed that participants who scored higher on the psychopathy-related trait of coldheartedness (which describes emotional detachment combined with an overall disagreeable disposition ) were less likely to fall prey to the contagious yawning stimuli. Interestingly, none of the other psychopathic traits showed this correlation. Related: 10 Women On The Best Thing Their Ex Taught Them People who rate highly on psychopathic traits tend to be generally uncaring, selfish, and insincere. So, while being low on empathy is part of psychopathy, it's not the whole picture. Psychopaths are also way more likely to be men than women, although there weren't any statistically significant gender differences in this study. Related: THIS Is The Best Age To Get Married (According To Science) If you're wondering whether or not your new friends are really as coldhearted as you think, this study suggests you might want to give 'em a good yawn and see what happens. Or, if that doesn't work, just count the selfies on their Instagrams.