You come home from work to find a grape-juice stain on your white couch. Your two kids deny any involvement. So who did it?

To find out, ask them separately what they think the punishment should be for whoever is responsible. If Tommy says, "No computer for a week," and Tammy says "No grape juice for a week," you probably have more work to do with Tammy.

This scenario is one of the many tips on ferreting out everyday fibs from the book "Spy the Lie: Former CIA Officers Teach You How to Detect Deception."

Michael Floyd and two fellow former ex-agents, with more than 75 years of interrogation experience between them, honed their methods on terrorists and criminals. But their advice works equally well on cheating spouses, lollygagging employees or schoolkids feigning illness.

"There are a lot of myths in the area of detecting deception, like avoiding eye contact," said Floyd in a recent telephone interview. "There are too many variables around it to be reliable. Research shows the opposite, that deceptive people tend to have better eye contact than those who tell the truth."

We all lie, on average 10 times a day, Floyd said: "This includes the social lies we tell to smooth our way through the day. If your significant other asks, 'Do you like this tie?' or 'Do I look fat?' of course there's only one answer."

There's also a general gender difference when it comes to reasons for lying. Men tend to lie to make themselves look better, while women want to protect the feelings of others, he said.

To detect a lie, start with being aware of the difference between where a truth-teller and a liar are coming from psychologically, Floyd advises.

"Facts are the truthful person's ally," he said.

Ask questions and pay attention to how quickly a person answers. "The untruthful person has to process the information, and that has an impact on their behavior," said Floyd. "They might repeat the question or say 'I'm glad you asked that.'"

Also, watch the person's body language. First, note his or her "anchor points," or where the arms and hands, feet and legs are positioned.

"If any of those anchor points change after the question is asked -- a hand to the ears or nose, rearranging objects on the desktop -- that's an indicator."

Restlessness alone, however, is no proof of a fabrication. Unnatural stillness may be even a bigger "tell."

Another verbal clue is the nonspecific denial, used by both Anthony Weiner and Martha Stewart in their high-profile scandals, he said. Weiner tried to deflect culpability by suggesting that someone else pretending to be him sent a lewd image over the phone. Stewart, on the other hand, made an overarching claim.

"When Stewart was asked if she had been involved in insider trading, her response was simply 'I'm innocent,'" Floyd said. "In our world, there's a big difference between 'I'm innocent,' which is a legal conclusion, and 'I didn't do it.'"

Smart questions

Another indicator that a person might be lying is when he or she is too convincing.

"If you are asked if you stole some money and you didn't, you're likely to simply say no, because the facts are your ally," said Floyd. "If you did do it, you may feel compelled to convince me you didn't. You might say, 'I'm an honest person, I would never do that, why would I risk my job over something so insignificant?' The untrained observer might think this makes you more convincing, but that's three deceptive indicators to us."

For instance, if you ask a child if she has any homework, a short "no" is much more believable than a tirade, such as "Don't you think I would be doing it if I had some? Why are you always nagging? Why don't you trust me?"

Floyd said that he needs to witness two indications of deception before he'll get serious about whether someone's lying: "We need to drill down and find out if they're telling a flat-out lie or just displaying a lack of confidence."

Often, getting to that point requires asking smarter questions: Instead of asking whether your child has homework, Floyd suggests you ask "How much homework do you have?"

Kristin Tillotson • 612-673-7046