When people find out I used to be a private investigator, the questions come in the same order every time.
Did you carry a gun? Did you ever get caught? And then, leaning in a little: So can you tell when somebody’s lying?
The honest answer disappoints everybody.
Mostly no. And neither can you.
The coin flip problem
This isn’t me being humble. Researchers have tested it hundreds of times. In 2006, two psychologists pulled together 206 studies covering roughly 25,000 people who were asked to sort truths from lies. The average score was 54 percent.
A coin flip gets you 50.
And the professionals? Cops, judges, people whose whole job is spotting liars? Not meaningfully better than everybody else. Experience made them more confident. It didn’t make them more right.
So where did we get the idea that a guy like me could look at your eyebrows and know?
Television.
The myth of the tell
Every crime show has the scene. The suspect glances up and to the left. He touches his nose. The detective narrows his eyes. Busted.
In real life, one gesture by itself means almost nothing. A nose rub is usually an itch. Crossed arms usually mean the room is cold. A guy who won’t look you in the eye might be lying, or he might be shy, or he might have been raised by a grandmother who told him staring was rude.
The best example I’ve got isn’t from my PI days. It’s from college.
I was doing my crime scene investigation internship, and the investigator I was shadowing warned me we had a court date coming up. This guy was confident. He knew his stuff, and he wasn’t shy about telling you so.
But before court, he pulled me aside. “Look,” he said. “I talk a big talk. But I am not good on the stand. I get so nervous.”
He wasn’t lying.
He got up there and did everything the crime shows say a liar does. The fidgeting. The twitching. Every tell in the book. He looked like a man holding a hand of random cards, trying to bluff his way into a royal flush.
And I knew, without a shadow of a doubt, that every word he said was true.
If I’d been sitting on that jury, I wouldn’t have believed him.
Honestly? It was awesome. This man I respected so much had a weakness. He was human. It was almost comforting.
It also taught me the most useful thing I know about lie detection. From the jury box, nervous and guilty look exactly the same.
What actually helps (a little)
If you want to get a few points above that coin flip, stop looking for one signal and start looking for a pile of them that agree with each other. And watch for the mismatch.
Somebody says “I’m totally fine with that” while their whole body slowly turns toward the door. Somebody says “yes” while their head is shaking no. Somebody laughs, but nothing else on them is laughing. That’s not proof of a lie. It’s a reason to ask one more question.
Which brings me to the real secret.
The lie detector that actually works
In PI work, nobody got caught because of their eyebrows. They got caught because of facts. Where the car was parked. What time the receipt said. Who walked out of the house, and with whom.
When we worked the case I told about in Excuse Me, Do You Know Where Foxfire Drive Is?, we never had to read the husband’s face. We just followed his car to Tennessee.
That case wasn’t special. Almost every cheating spouse case I worked went the same way.
Here’s the part that surprises people. The person who hired me already knew. Every time. They were 100 percent right. I never worked a cheating case where I discovered something the client didn’t already know.
Sometimes I could add a detail, like where the new boyfriend lived. Because sometimes it wasn’t another woman at all. It was a guy. But the main thing? They already had it right. I was just there to hand them the proof.
And they didn’t figure it out from a twitch or a nose rub. They figured it out because the story didn’t match. He said he was at X. He was at Y. Over and over, until the pattern was louder than anything his face could hide.
It wasn’t glamorous. Most of the job was comparing where somebody said they’d be with where they actually were.
Which is why I’ll go ahead and say something that’s going to make a few people mad. If your spouse won’t share their location with you on Find My, or whatever the Android version is, you should just go ahead and end that relationship.
That’s how it played out in every case I ever worked. Every single one.
The part nobody likes to hear
Part of the reason we’re so bad at lie detection is that we want to believe people. In those same studies, folks labeled most statements as true, even when they weren’t.
I used to think that was a weakness. I don’t anymore. A world where everyone assumed everyone else was lying would be a miserable place to live. Neighborhoods, churches, and marriages all run on giving people the benefit of the doubt.
So here’s my professional advice, from someone who did this for a living. Look for mismatches. Ask the follow-up question. Check the facts. Quit staring at people’s eyebrows.
And if somebody ever tells you they can always tell when you’re lying?
That’s the lie.
More from the PI years: how I talked my way into the job in From Ninja to Private Investigator, and what stakeouts are really like in What Ninja Training Actually Taught Me About Surveillance.
There’s always a story under the story.
If this one stuck with you, I’ll send the next one straight to your inbox.