If you ever need to, there may be a simple way to spot a psychopath - if you're not a qualified psychiatrist.
People with psychopathic tendencies are less likely to yawn after seeing someone else yawn, one recent study found.
This trait is linked to empathy, a characteristic seemingly absent in psychopaths.
Mr Brian Rundle, the lead author of the study, published in Personality and Individual Differences, said:
The take-home lesson is not that if you yawn and someone else doesn’t, the other person is a psychopath.
A lot of people didn’t yawn, and we know that we’re not very likely to yawn in response to a stranger we don’t have empathetic connections with.
But what we found tells us there is a neurological connection — some overlap — between psychopathy and contagious yawning.
This is a good starting point to ask more questions.
If this test doesn't work, Dr Daniel Boduszek of the University of Huddersfield devised 20 questions which may get you closer to finding out.
The questions, which ask people the extent to which they agree with statements such as:
I know how to pay someone compliments to get something out of them
I sometimes tell people what they want to hear to get what I want from them
I am good at predicting how someone will feel
I know how to make another person feel guilty
...could give a marker of psychopathic tendencies based on the amount of egotism someone exhibits when answering - or so Boduszek claims.
If it's all about them, this could reveal a psychopathic lack of empathy.
So the next time you're with a Patrick Bateman wannabe, you have a few tests at your disposal.