While many of us are huge fans of true crime and know the ins and outs of murder cases, it's safe to say that the majority of us probably wouldn't be able to tell if a murderer was standing right in front of us.
When it comes to a murderer, we might think of the obvious 'signs', such as anti-social behavior, not making eye contact and tripping over words.
But an expert has weighed in with the actual signs you should be looking out for which may mean you're stuck in a conversation with a serial murderer.
Cliff Lansley explained that instead of the big personality faults we usually look out for, killers often give themselves away with tiny details.
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Speaking to The Hippocratic Post, he said: "Even the most confident, hardened killers can give themselves away with tiny signs and gestures from the face, body, and voice that suggest that they are lying.
"The key is to know what you are looking for – the reliable indicators of deception."
It goes without saying that these traits don't absolutely guarantee a serial killer, but they certainly are common.
So, if you want to know whether or not somebody is lying about being a killer, there's a simple way to get the truth.
It's not whether or not they avoid eye contact, begin to sweat or avoid questions.
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Lansley suggested setting a foundation of truth: "We talk about things that are safe and true, such as their family, skills, education and hopes and dreams.
"During that period, we note how often they blink, the normal colour of their skin, their speech rate and how they maintain eye contact.
"Later on, when the real questioning begins, we can assess changes to these normal baseline patterns to assess discomfort, stress and lying."
Some criminals may use eye contact to judge whether their interrogator is buying their lies, while others may avoid it altogether.
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Linguist John Bowden added: "Breaks in eye contact indicating deception are generally accompanied by additional deceptive body behaviour."
This highlights the importance of looking at body language comprehensively, rather than just taking one nonverbal sign out of context.
It is important to note that every person is unique and will demonstrate varying cues under pressure – which is what makes reading body language so tricky.
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So, in case you were looking to catch someone out, the way to tell if someone is lying is finding their truthful, baseline expressions and notice how they change during questioning.
In general, though, it's probably best to leave it to the professionals.
Topics: Crime, True crime, Psychology