A FRIEND
Assuming you know this person quite well, you will be familiar with their usual facial expressions - the way they smile, laugh, their posture and the amount of eye contact they use when they engage with you.
You recognise their mood, especially in a relaxed, social setting. It may be a few – a cluster - of facial micro-expressions – that will give them away.
They maybe blushing or have a reddening of the face, caused by anxiety.
Their nostrils may flare, they might nibble or lick at their lips and avoid direct eye contact or blink rapidly. You just KNOW that something isn't quite right.
A WORK COLLEAGUE
Unlike a friend who is familiar in a personal setting, a work colleague, who may mask their real feelings in a professional environment, maybe trickier to spot lying.
It's worth looking at body language gestures, rather than facial expressions, in someone you don't know so well. They may use their arms and hands more expansively – or much less so - than usual.
It's the change from usual behaviour that is the thing to look out for here.
It's also worth noting any change in their speech pattern – if it's speeding up or slowing down, or the pitch is more variable than you recall, they may well be not speaking the truth.
A RESTAURANT OR SHOP WORKER
The chances are that you may not have met this person before, or rarely, so you don't have so much to go in calling them out as bluffing.
Someone in a chance encounter like this, who may well be protecting themselves or their business, with a lie to avoid a difficult situation, will tend to go into a fairly verbose and possible complex reason for why they are unable to do something.
This is buying them some thinking time and an attempt to confound you.
They are unlikely to use the pronouns 'I' or 'me', preferring to psychologically distance themselves, in a direct sense, from their untruth by using 'we' or 'they', pushing the responsibility onto their employers.
A STRANGER IN THE STREET
Maybe you are asking for directions or someone has approached you to mention something they have seen.
You have no previous experience to go on at all, so you can only really go on what they say, rather than their non-verbal gestures.
A big give away is that they will repeat a word or phrase to you. So, if you ask for the way to Victoria train station, they will repeat it back to you as a question.
They are buying time here to decide whether to tell you they don't know, take a lucky guess or simply misdirect you.
They may also provide way too much detail to try and prove to you that they know what they are talking about even if they don't.
YOUR PARTNER
Given that you probably know your partner more intimately than anyone else in your life, it's tempting to think that you would also be most likely to know when they are lying to you. But actually, the opposite is true.
It can be much harder to tell if someone really close to you is lying, simply because the trust and belief that we place in them is often so implicit, that we wouldn't want to think that they were telling anything but the truth.
They key things to look out for in a partner lying to you are changes in their behaviour which become more noticeable – they become more secretive, less affectionate or simply avoid eye contact.
The reverse of this could be the case – it's the changes in behaviour as much as the behaviour itself.
They may also become highly defensive, telling you that you that they'd never lie to you or even project onto you and accuse you of lying in order to cover up for themselves or justify their own actions.
They may get angry or they may seem very calm and considered. It's clusters of change in behaviour that will give them away.
