On January 27, 2008, Penny Boudreau’s twelve-year-old daughter, Karissa, went missing in her hometown of Bridgewater, Canada. That afternoon, mother and daughter had had a fight in a grocery-store parking lot. They’d been having a “heart-to-heart” about “typical teen-age things,” Boudreau said. At 7:30 P.M., Boudreau, worried, called a few friends and teachers—none had heard a thing—and notified the police. By the following day, Karissa was still unaccounted for and the Bridgewater police began notifying other precincts. They issued a media alert and began a full search effort.

On January 29th, the police station held a press conference. Penny, distraught, pleaded for her daughter to return, in a widely televised appeal. On February 1st, she repeated her plea. Anyone with any knowledge of her daughter’s whereabouts, she begged, should make immediate contact. The search parties widened, and local residents joined law enforcement to help track the girl they were now calling “Bridgewater’s daughter.” Still, Karissa remained missing.

On February 9th, two weeks after her disappearance, Karissa was finally found. A woman had pulled over along the side of Highway 331—the road that makes its way along the LaHave River, through Bridgewater—to let her nine-year-old son go to the bathroom out of sight of the passing cars. She rushed to his side when he began screaming: out of the snow, right on the bank of the river, he could see a set of human toes. Bridgewater police soon positively identified the body as Karissa Boudreau. She was naked from the waist down, her body frozen solid by the winter cold, a pair of white Winnie-the-Pooh underwear down below her knees. Five days later, the police announced that the missing-person case had officially become a homicide investigation.

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People lie all the time. According to the psychologist Robert Feldman, who has spent more than four decades studying the phenomenon, we lie, on average, three times during a routine ten-minute conversation with a stranger or casual acquaintance. Hardly anyone refrains from lying altogether, and some people report lying up to twelve times within that time span. I might open a conversation, for instance, by saying how nice it is to meet someone—when I’m really not at all happy about it. I might go on to say that I grew up in Boston—a lie, technically, since I really grew up in a small town about forty minutes outside the city. I could say that the person’s work sounds fascinating, when it’s no such thing, or compliment him on his (drab) tie or his (awful) shirt. And if the person mentions loving a certain downtown restaurant where I’ve had a terrible experience? I’m likely to just smile and nod and say, Yes, great place. Trust me: we often lie without giving it so much as a second thought.

We lie in most any context—Feldman’s work has turned up frequent lies in relationships ranging from the most intimate (marriage) to the completely casual. Some lies are small (“You look like you’ve lost a bit of weight”) and some bigger (“I did not have sex with that woman”). Sometimes they are harmless, and sometimes they are not.

Many of us believe that we can tell when someone else is lying, and, over the years, a folklore has developed around the facial and physical cues that can give someone away. Liars don’t look you straight in the eye. When someone is lying, he looks up and to the side, as if searching for something. A liar fidgets and seems somehow nervous. Sometimes, he’ll scratch or pull his ear. He’ll hesitate, as if he’s not sure he wants to tell you something. These, however, are all “old wives’ tales,” Leanne ten Brinke, a psychologist at the University of California at Berkeley whose work focusses on detecting deception, told me. “The empirical literature just doesn’t bear that out.”

The mismatch between our conception of a liar and the reality—that there’s no “Pinocchio’s nose,” as ten Brinke put it—is surely one reason that, despite our confidence, our ability to tell a lie from the truth is hardly different from chance. The psychologist Paul Ekman, professor emeritus at U.C. San Francisco, has spent more than half a century studying nonverbal expressions of emotion and deception. Over the years, he has had more than fifteen thousand subjects watch video clips of people either lying or telling the truth about topics ranging from emotional reactions to witnessing amputations to theft, from political opinions to future plans. Their success rate at identifying honesty has been approximately fifty-five per cent. The nature of the lie—or truth—doesn’t even matter.

Over time, Ekman did find that one particular characteristic could prove useful—microexpressions, or incredibly fast facial movements that last, on average, somewhere between one-fifteenth and one-twentieth of a second and are exceedingly difficult to control consciously. Those, however, were too fleeting and complex for any kind of un-trained expert to spot: out of Ekman’s fifteen thousand subjects, only fifty people could consistently point them out.

To ten Brinke, something about the existing narrative of deception didn’t quite make sense. Why would we be so bad at something that was so necessary? If the only predictive signs of deception took so much time and energy to learn, that wouldn’t make them of much use. “It didn’t fit well with our evolutionary perspective of human development,” ten Brinke says. “Wouldn’t it have been helpful for us to be able to detect lies and cheats?”

Maybe the untrained “us” wasn’t so bad at lie detection as all that. It could instead be the case that researchers had simply been asking the wrong questions. It wasn’t conscious lie detection, a forced, yes-or-no judgment, that mattered. Maybe, instead, our ability lay in our unconscious perception: in our sensing something if we weren’t looking for it, something that might disappear if we tried to probe it head on. “For lie detection to be an adaptive skill, that helps us to avoid liars and befriend truth-tellers, it doesn’t have to be conscious alarm bells. It could be more subtle,” ten Brinke says. “More of a feeling that you don’t really want to lend this person twenty dollars, that you’re not excited to go on a second date with this guy.” Ten Brinke and her colleagues decided to focus their efforts on finding evidence for unconscious lie detection.

In a series of studies, out this month in the journal Psychological Science, the Berkeley team had students watch a video of a possible criminal who was being questioned about stealing a hundred dollars. As in an actual interrogation, the suspect responded to both baseline questions (“What are you wearing?” “What’s the weather like outside?”) and target questions (“Did you steal the money?” “Are you lying to me right now?”). Half of the potential criminals were lying; half were telling the truth. Each participant watched one truthful and one deceptive video.

Next, the students completed a simple assessment: Were the pleaders in the videos telling the truth? Just as in prior studies, ten Brinke’s subjects, when asked direct questions, did no better than chance at determining who was truthful and who wasn’t.

But then the students participated in one of two unconscious lie-detection tasks. In each, they saw still photos of the two pleaders alongside words that were associated with either truth, such as “honest” and “genuine,” or lies, such as “deceitful” and “dishonest.” Their goal was to categorize the words as indicative of either truth or lies, as quickly and accurately as possible, regardless of the face they saw along with it. If “genuine” flashed on the screen, they would press a button to classify it as a truth-category word as soon as possible.