How to tell when someone's lying

We've all told tall stories, porkies, fibs or whoppers from time to time — to make life a little easier or get ourselves out of trouble, right?

But who are we really trying to kid? If you make a habit of telling lies you're on a one-way street to trouble. If you tell a really big porky pie, you could even end up in a holding cell.

The bad news is that most of us lie more than we imagine. "The fundamental feature of liars is that they are manipulative, they deny another person truthful information," says Dr Joseph Forgas, Professor of Social Psychology at the University of New South Wales.

He says when it comes to lying, men and women have different agendas. "Men might more often lie about things like financial status, women might lie more about trying to make themselves more attractive."

There are also different levels of lies — the harmless variety is the white lie — considered to be "lies which don't have serious consequences but help us to make social relationships work. If you were to be totally brutally honest all the time, to everybody around you, you become very unpopular very quickly," says the professor.

But the lies which cause the most harm to ourselves and others, are the anti-social lies deliberately aimed to damage someone else.

"I think very often people lie more for ego defensive reasons, you want to avoid blaming yourself, you want to avoid being considered negatively by others," says Dr Forgas.

To find out more about the dangers of lying, a visit to the Los Angeles Police Department is in order. Roy Orbitz is the supervisor of the LAPD's lie detector unit.

Can Leila beat the polygraph? According to Roy, there's no chance. So Roy wires Leila up so he can monitor changes in her physiology — breathing patterns, blood pressure, pulse rate and sweat glands.

"I feel like I'm in the electric chair," says Leila.

Roy believes that he can catch Leila out with one simple question — provided that she lies.

Roy: Regarding where you were born, were you born in France?
Leila: No.
Roy: Were you born in Australia?
Leila: No.

Leila's only got one birthplace, so most of her 'no' answers are true.

Roy: Were you born in Iran?
Leila: No.

Now that's a lie — Leila was born in Iran, and Roy caught her out straight away with the polygraph revealing the truth.

"You're wondering maybe how I can tell?" says Roy. "I can tell Leila didn't tell me the truth, due to blood pressure change, skin resistance, a pattern change in her breathing all together added up."

The main thing Leila learned from her session on the polygraph is that lying can be pretty stressful. But Dr Forgas says if she lied often enough, stress wouldn't be an issue. "I think that if you happen to be a habitual liar you'd probably get used to lying and so no longer have those sort of stress signals, so I think lying is probably not physiologically damaging to your health. It's much more likely to be socially damaging. "The greatest cost of lying is that it destroys trust if you get found out. If you think about it, all human social relationships function because we have trust in each other, we accept that other people are going to be honest and truthful with us. So when you find out that somebody lied to you, it kind of totally destroys the trust toward that person and that's a huge social cost, because it does make relationships difficult to maintain afterwards."

So how can we spot a liar? Dr Jo-Ellan Dimitrius reads body language for a living — she even helps select jurors and witnesses in court cases and has worked on some famous cases, including the OJ Simpson trial.

What are Leila's chances of fooling Dr Dimitrius when she lies? As they talked together Leila's slips in some fibs to see if Dr Dimitrius can pick them up.

Dr Dimitrius: Do you live in LA?
Leila: Yes.
Dr. Dimitrius: How long have you lived here?
Leila: A year.
Dr. Dimitrius: And where did you live before that?
Leila: I lived in Melbourne.
Dr. Dimitrius: Any brothers or sisters?
Leila: Yes, I've got one brother.
Dr. Dimitrius: And what does he do?
Leila: He's in, um, computer programming.

Does our body language betray us when we lie? Can Dr Dimitrius spot Leila's real lies, just by observing body language?

Dr. Dimitrius: "Are you a sports person? Are you active?"
Leila: "Yes, I like to play indoor netball and I do indoor soccer, and I also work with a trainer."

Did Dr Dimitrius spot the lie?

Dr Dimitrius: The first one that I think I may have caught you on is the sports.
Leila: Yes, I do do some sports.
Dr Dimitrius: I think that you may have blinked your eyes a lot faster and even leaned in, which often times we see with behaviour of people who aren't being forthcoming. They want to take you into their personal environment and pull you into their lies. Leila: Okay, I don't play netball or soccer so you got me!
Dr. Dimitrius: When I asked you about your siblings and you said you had a brother, then when I asked you if he was older or younger, you said he was younger and he was 30. Is that true?
Leila: Yes, that one's true.

So that's one apiece. But if you suspect someone is lying to you, here are a few vital clues to look out for:

• Are they blinking their eyes a lot?
• Are they avoiding direct visual contact?
• Are they licking their lips a lot?
• Are they putting their hand up to their face?
• Are they having trouble with getting it all out?

Well, that's body language and lying, but what should you do when your children lie? Is it something you should be worried about and how should you deal with it? And how old are kids when they start lying?

"Two-year-olds lie sometimes, but are usually honest. By three, kids get very good at lying and they continue to increase as they get older. It's completely normal," says Thomas Lyon, a professor of Law and Psychology at the University of Southern California.

So what do we do with kids when they start telling lies? "The main thing is not to punish a child if they admit to wrongdoing. If you always punish them every time they admit to doing something wrong, they'll quickly learn not to admit to doing things wrong and that's when they really start to lie more frequently," Professor Lyon says.

How can we get our kids to be more truthful? The best thing parents can do is to lead by example, because children are watching us every step of the way. "Children often learn by what they see parents doing. So, if you live up to your statements, then children are more likely to live up to theirs," says Professor Lyon.

So what do you do if you've missed the boat and your child's turning into a compulsive liar? According to Professor Lyon sometimes children get into telling tall tales and they get to the point where everything they say is exaggeration. "Sometimes it's important to sit down with a child like that and say 'there are some times where it's really important to tell the truth'. And to explain that when serious things have happened, that the truth is most important."

So both kids and adults tell lies — they're an inevitable part of life. But bear in mind that the more lies you tell, the more your problems multiply. Ask any pathological liar and they'll tell you, the hardest part is remembering all the yarns they've been spinning. It's when they forget, that they get caught out in their own web of deceit. So honesty really is the best policy.

Now one place where lying can be dangerous is when talking to your doctor. Don't try to be the perfect patient by understating your ailments or overstating your health. They can only help you if they know all the facts.

Fast facts

• How often do people lie to partners about previous relationships? According to one American study an astonishing 85 percent of the time — think about that next time you go on a date!