How to spot a lie

There is an enormous amount of nonsense written about detecting lies. Most of it takes the form of a list: liars look up and to the left, liars touch their nose, liars cannot hold eye contact. It is satisfying to read and close to useless in practice.

Here is the honest position, including the parts that are less fun.

The myth worth killing first

Liars avoid eye contact. You have heard it your whole life, and it is backwards more often than not.

Someone who has decided to lie to you is usually managing their behaviour. They know the stereotype as well as you do. So they hold your gaze, steadily, for slightly too long, because they are working at appearing credible. Meanwhile the honest person recalling something genuinely difficult often looks away entirely, because recall and eye contact compete for the same attention.

Sustained, deliberate eye contact is not evidence of honesty. Occasionally it is the opposite.

What is actually worth watching

Not individual gestures. Changes.

Everybody has a baseline: their normal rate of speech, their normal amount of movement, how much they usually fill silence. A tell is not a gesture from a list. A tell is a departure from that person's own baseline, at the moment a specific subject arrives.

Which means the useful question is never "is this person a liar". It is "why did that change, just then".

• Timing. A pause in the wrong place is worth more than any gesture. Truth is usually recalled. Lies are usually constructed, and construction takes time.
• Effort. Watch for the moment answering visibly costs more than it did thirty seconds earlier.
• Detail that moves. A rehearsed story tends to be told the same way twice. A real memory gets told differently, because the person is re-remembering rather than reciting. Counter-intuitively, suspiciously consistent is more suspicious than slightly inconsistent.
• Distancing language. People shed ownership when uncomfortable. "I did not do that" becomes "that did not happen".

The technique that beats all of it

Ask them to tell it backwards.

Recounting a genuine memory out of order is awkward but perfectly possible, because you are describing something you actually experienced. Recounting an invented story out of order is extremely hard, because the story was built forwards and does not exist as a memory to be re-entered at the middle.

It is not theatrical, and it will never make good television. It is simply far more reliable than watching someone's hands.

The part people do not want to hear

Even trained, even paying full attention, nobody reads deception with anything like the accuracy the books promise. Study after study puts human lie detection barely above chance, and that includes people who do it professionally.

What training genuinely buys you is not certainty. It is better questions, and a much healthier scepticism about your own instincts. The most dangerous person in a negotiation is the one who is certain they can tell.

Which brings me to the useful application. Reading people well is worth far more in the ordinary moments than in the dramatic ones: noticing that a client has gone quiet on price, that a colleague agreeing to a deadline is not confident about it, that a room has stopped following you. That is where it pays.