You are sitting at home, watching TV. You yawn. Your partner tries to resist, but can't, and soon he or she yawns, too. It's not just in your head: Yawning is contagious, not just in humans but in many species. It's even contagious between us and our dogs. 
Empathy is one of the core psychological factors that leads to catching yawns , a critical point underpinning a new study  indicating that psychopaths may be immune to contagious yawns. Psychopathy is defined, in part, by a lack of empathy. Could this make people with the trait impervious to their peers' yawns?
Researchers at Baylor University had 135 subjects take the Psychopathic Personality Inventory-Revised (PPI-R) and then exposed them to a contagious yawn experiment (this, apparently, is a thing, which is awesome). The Coldheartedness part of the psychopathy scale was strongly tied to whether the person yawned. The more coldhearted a person was (i.e., the less empathetic), the less likely they were to catch a yawn.
A lack of empathy has already been known to relate to immunity to contagious yawning. Studies have shown, for example, that children on the autism spectrum are less likely to catch a yawn . But this is the first study to show its link to psychopathy.
Empathy may not be the only trait at play. Psychopaths also exhibit fearlessness as a typical trait. The researchers tested their subjects to measure how easily they startled; psychopaths would startle less. They found that the less likely someone is to startle, they less likely they are to catch a yawn.
Of course, this is not a diagnostic tool for psychopathy, but it is an interesting connection, showing how these personality traits affect various behaviors in unexpected ways.*
So, if you yawn and your partner never seems to yawn back, reflect for a moment on his or her empathy in other situations, and consider if something more serious may be lurking.
* This post has been a bit of a departure from this blog's normal Internet focus, but the study is so cool that I had to share. However, the fact that traces of these personality traits appear in many types of behavior is exactly the kind of thing we computer scientists rely on to infer things about people from their online activities!
 Joly-Mascheroni, Ramiro M., Atsushi Senju, and Alex J. Shepherd. "Dogs catch human yawns." Biology Letters 4.5 (2008): 446-448.
 Rundle, Brian K., Vanessa R. Vaughn, and Matthew S. Stanford. "Contagious yawning and psychopathy." Personality and Individual Differences 86 (2015): 33-37.
 Giganti, F., & Esposito Ziello, M. (2009). Contagious and spontaneous yawning in autistic and typically developing children. Current Psychology Letters, 25(1) (Online, URL: http://cpl.revues.org/index4810.html).