Yet the more psychologists looked, the more elusive any reliable cues appeared to be. The problem is the huge variety of human behaviour. With familiarity, you might be able to spot someone’s tics whenever they are telling the truth, but others will probably act very differently; there is no universal dictionary of body language. “There are no consistent signs that always arise alongside deception,” says Ormerod, who is based at the University of Sussex. “I giggle nervously, others become more serious, some make eye contact, some avoid it.” Levine agrees: “The evidence is pretty clear that there aren’t any reliable cues that distinguish truth and lies,” he says. And although you may hear that our subconscious can spot these signs even if they seem to escape our awareness, this too seems to have been disproved.

Despite these damning results, our safety often still hinges on the existence of these mythical cues. Consider the screening some passengers might face before a long-haul flight – a process Ormerod was asked to investigate in the run up to the 2012 Olympics. Typically, he says, officers will use a “yes/no” questionnaire about the flyer’s intentions, and they are trained to observe “suspicious signs” (such as nervous body language) that might betray deception. “It doesn’t give a chance to listen to what they say, and think about credibility, observe behaviour change – they are the critical aspects of deception detection,” he says. The existing protocols are also prone to bias, he says – officers were more likely to find suspicious signs in certain ethnic groups, for instance. “The current method actually prevents deception detection,” he says.