You can't grab, poke, or jab "the truth," and people tend to rely on analogies when describing intangible concepts. Like Julian Assange, the founder of WikiLeaks, many people seem to conceive of the truth as a liquid. When truth escapes, it seeps or leaks, rather than rampaging like a bull or hurtling like an avalanche. Metaphors aren't always appropriate, but in this case the truth suppressed behaves very much like water trickling from a breached dam. Some people are better at keeping the truth at bay than others, but there are telltale signs that suggest that it may be heaving against the dam wall of dishonesty. Plenty has been written on the question of truth (and lie) detection--especially on how poorly we detect deception and, consequently, how to improve your chances of picking liars from truth tellers--but I'll focus on a couple of interesting and (mostly) recent findings that suggest that leakage is inevitable and detectable, as long as you know where to look.
We tend to assume that most of what we hear is true, unless we adopt an unusually skeptical, vigilant, or suspicious stance. Unfortunately, the people we tend to to trust are often the ones who deserve extra scrutiny--particularly when those people are men. On the one hand, research suggests that attractive men with symmetrical faces appear more trustworthy than relatively unattractive men; on the other hand, attractive men with wider, more masculine faces, are in fact less trustworthy than those with narrower faces. Michael Stirrat and David Perrett, at the University of St. Andrews in Scotland, found that men with wider faces tended to exploit their partners in games of financial trust, more often absconding with money that they were entrusted to return later in the game. Stirrat and Perrett argued that untrustworthy men are more likely to have wider faces than trustworthy, because both facial width and trustworthiness are determined to some extent by testosterone levels. Testosterone happens to both accentuate the width of a man's face and increase aggression and deceitful behavior, so the men with wider, hypermasculine faces were also more likely to betray their partners' trust.
Biological markers are difficult to hide, but even strategic attempts to disguise the truth sometimes fall short. Mitja Back and several of his colleagues in Germany and the United States collected over 200 social networking profile pages, some from Facebook and some from a similar German site called StudiVZ. Facebook's half a billion users spend an average of one hour actively perusing the site each day, which is often more time than they spend interacting with friends in the flesh. Profile pages are therefore an important source of social self-promotion, and users commensurately agonize over which photos, books, TV shows, musical artists, quotes, and self-descriptions to mention and which to strategically omit. Back and his colleagues recognized the self-promotional function of social networking, so they examined whether profile pages fulfill this aim, or whether they instead paint an accurate depiction of their owners' personalities, warts and all. When they asked the pages' owners to describe themselves as they "ideally would like to be," they found no relationship at all between these idealized self-images and the content of the users' profile pages. For example, when strangers rated each profile page, users who wanted to appear adventurous appeared no more adventurous than users who preferred to appear relatively timid. In contrast, when the researchers asked four close friends to describe each user, the descriptions mapped onto the users' profile pages quite neatly. Put simply, if a Facebook user's friend thinks he's a bit neurotic and not particularly friendly, but he'd like to appear calm and outgoing, chances are that his Facebook profile tells a sorry tale of neuroticism and disagreeableness. Even at our most strategic, we can't help revealing our true selves. The brief paper that described these results was necessarily light on theory, but this fascinating result is consistent with other studies that show how often we're unable to conceal our true selves.
The business of detecting dishonesty has moderately high stakes in the context of economic trust games and social networking, but the stakes are much higher in the world of crime and punishment. Even experts are notoriously incapable of distinguishing truth tellers from active deceivers, though Dutch researcher Aldert Vrij has suggested one technique that seems to tip the balance in favor of otherwise hapless truth seekers. The art of deception requires considerable mental resources, in large part because it's easier to keep threads of truth untangled than it is to weave and integrate new strands from scratch. Not only does the fictional story have to progress logically, but each new component must remain consistent with its earlier counterparts. Many serial deceivers are capable of stringing together a coherent story, but Vrij made two clever suggestions that seem to ferret out even hardened hucksters: ask them to look you squarely in the eyes while recounting the story backwards. Looking someone in the eyes is taxing in isolation, but pair that sobering experience with the task of reconstructing the story in reverse, and signs of deception rise to the surface. Under these conditions, liars fidgeted more vigorously than truth tellers, and showed obvious signs of nervousness. In one experiment, police were capable of detecting liars 60% of the time when they told stories in reverse, but only 42% of the time when they told similar stories chronologically. An accuracy rate of 60% isn't flawless, but it's better than the 50% (or lower) accuracy rates that researchers typically find in deception detection studies. The policemen were also marginally better at detecting truth tellers when truthful stories were recounted backwards rather than forwards.
The truth has a way of seeping through minute cracks in the armature of deception, but you have to know where to look to spot these signs of dishonesty. Sometimes the clues are biological, many persist even when we're ardently trying to hide them, and applying mental pressure to would-be deceivers seems to illuminate their falsehoods the more so.
Vrij, A., Mann, S. A., Fisher, R. P., Leal, S., Milne, R., & Bull, R. (2008). Increasing cognitive load to facilitate lie detection: The benefit of recalling an event in reverse order. Law and Human Behavior, 32, 253-265.
Back, M. D., et al. (2010). Facebook profiles reflect actual personality, not self-idealization. Psychological Science, 21, 372-374.
Stirrat, M., & Perrett, D. I. (2010). Valid facial cues to cooperation and trust: Male facial width and trustworthiness. Psychological Science, 21, 349-354.