Everybody's told a white lie at least once. Lying is one of those behaviors that's given us an evolutionary advantage over millennia; we lie to maintain our relationships, help others, save ourselves from embarrassment and generally try to preserve our place in society. But just as humanity is skilled at lying, we're also always trying to detect who's lying to us. And it's not nearly as easy as you might have assumed. Your grandmother might have claimed she could always tell you were fibbing because your ears turned red, but in reality, humans are very practiced at deception, and being able to tell if someone's lying to you isn't a simple task.
We learn to lie pretty early in life — from around the age of two or three, according to scientists. But, as parents and preschool teachers will tell you, early lies are very different to sophisticated lies in later life. Children may lie, but they won't necessarily have built up back-up lies to maintain the deception, so further questioning generally pulls it all to the ground. "Did you steal Charlie's chocolate bar?" "No." "Where did you find the chocolate bar?" "It was in Charlie's pocket." Busted. As we grow, however, we learn how to dissimulate with more elegance. And there's no certain way to detect a fib for sure without a confession.
"Lie detector" or polygraph tests, which detect the heart rate as a person is asked questions, have always been popular on TV and in the movies, but in real life they're regarded with a lot of suspicion. The American Psychological Association explain that, based on research on their accuracy, there is "little basis for the validity of polygraph tests," though experts are always trying to make them more accurate and detect more variables, like how the nervous system reacts. It's actually really, really hard to detect what a human body's "tells" are when you're lying. One study suggests that most of us can only detect a lie around 60 percent of the time. It's much better than zero, but it's also far from a perfect success rate.
And research into lying "signals" hasn't resulted in slam-dunks, either. For several years the belief that eyes could hold the key to lying — that if you look to the upper left you're telling the truth, but to the upper right if you lie — held some sway. However, it's been really difficult to replicate that result, and research in 2012 found that it didn't hold up in tests, whether people knew about the supposed eye-trick or not. In fact, "real" liars know that you're expecting them not to look at you, so will make sure they do, while truth-tellers often won't even think about it and will stare off elsewhere while they're concentrating on telling you what happened. If somebody tells you a sure-fire way to know if somebody's lying, chances are they're not exactly telling the truth themselves.
So how can you detect a lie? The good news is that humans seem to have a good unconscious ability to detect lying, even if they don't translate that into conscious thought; a study by the Association For Psychological Science in 2014 found that, even if we don't 'click' that a person is fibbing, we can often pick up on signals that they are.
There are also other cues. According to an overview of some 60 studies on deception behavior by American scientists in 2011, you can tell a person's lying by talking to them more about their story. If somebody's lying, the scientists noted, they don't over-elaborate, keep things simple and short, justify themselves without being prompted, repeat questions before answering them, slow down their answers, and monitor your reaction as they're spinning their tale, to make sure you're going along with it. Don't believe that most liars are effusive and have an easy answer for everything; they're actually likely to restrict themselves to a single set of facts rather than elaborating.
And if you want to be a good lie detector, it's actually not a good idea to be suspicious of everybody. Oddly enough, research in 2010 found that people who are more trusting in general, with a high belief in other peoples' inherent desire to tell the truth, are actually better at detecting when they're being lied to. Cynicism isn't a street-smart trait; it may actually make you more inaccurate at noticing deception, possibly because you see it everywhere.
So if you want to know that somebody's lying to you, trust that they might be telling the truth, get them to recheck and retell their story, and don't hold onto old wive's tales. If you're telling a white lie yourself, try not to squirm and be as elaborate and effusive as you can (though obviously honesty is the best policy). And if you end up still being uncertain if that vase really did get broken by a gust of wind, don't worry; short of a confession, there's no realistic way to tell for sure.