^{Getty/Cindy Ord}

Ever notice how when someone swears to tell the truth in a court of law, they put one hand on a religious text and raise their other hand into the air, palm facing whoever they're speaking to? 

That's because, the Peases write in "The Definitive Book of Body Language," an open palm has been associated with "truth, honesty, allegiance, and submission" throughout Western history. 

"Just as a dog will expose its throat to show submission or surrender to the victor," they write, "humans use their palms to show that they are unarmed and therefore not a threat." 

If their voice goes up or down, they're likely interested

Whether you know it or not, your vocal range shows your interest.

"Once a conversation begins, besotted women slip into sing-songy voices," Psychology Today reports, "while men drop theirs an octave." 

^{amber litzinger/flickr}

The jury is still out on whether we can tell when someone is faking what scientists call a Duchenne smile. It's the expression we make when we're genuinely experiencing positive emotion.

At one point, researchers believed that making a genuine smile was nearly impossible to do on command. The smile, they said, was all about the crow's-feet around your eyes. When you're smiling joyfully, they crinkle. When you're faking it, they don't. 

If someone's trying to look happy but really isn't, you won't see the wrinkles.

More recently, a study found that people could do a pretty good job of faking a Duchenne smile, even when they weren't feeling especially happy.

It seems safe to say that if the crinkles aren't there, the person's probably not genuinely happy. But just because the crinkles are there doesn't necessarily mean they're elated.

Raised eyebrows are often a sign of discomfort

In the same way that real smiles shape the wrinkles around your eyes, University of Massachusetts professor Susan Krauss Whitbourne says worry, surprise, or fear can cause people to raise their eyebrows in discomfort.

So if someone compliments your new hairstyle or outfit with their eyebrows raised, it may not be sincere.

^{Thomson Reuters}

If someone is closing their palm and pointing with their index finger, then they're trying to display dominance, though it doesn't always work out. 

"The Palm-Closed-Finger-Pointed is a fist where the pointed finger is used like a symbolic club with which the speaker figuratively beats his listeners into submission," the Peases write. "Subconsciously, it evokes negative feelings in others because it precedes a right overarm blow, a primal move most primates use in a physical attack." 

If they mirror your body language, the conversation is probably going well

When two people are getting along, their postures and movements mirror each other's. When your best friend crosses her legs, you will, too. If you're on a date that's going well, you'll both be making the same goofy hand gestures. 

This is because we mirror each other when we're feeling a connection, says positive psychologist Barbara Fredrickson.

^{Business Insider}

In an attempt to avoid looking shifty-eyed, some liars will purposefully hold their gaze a touch too long, so that it's slightly uncomfortable, according to behavioral analyst and body language expert Lillian Glass. 

They may also stand very still and not blink.

Eye contact shows interest — both positive and negative

When you look someone in the eyes, it sets an arousal state in the body. 

"How that arousal is interpreted, however, depends on the parties involved and the circumstances," writes Claremont McKenna College organizational psychologist Ronald E. Riggio.

"Being stared at by a stranger who appears large or ominous can be seen as a threat and elicit a fear response ... However, the gaze of a potential sexual partner causes arousal that can be interpreted positively — as a sexual invitation." 

^{Getty Images}

How people hold themselves is a big clue to how they're feeling.

If someone's leaning back and relaxed, they probably feel powerful and in control. In fact, research has found that even people born blind raise their arms in a V shape and lift their chins slightly when they win a physical competition.

On the other hand, a low-power pose — seen when someone closes up and wraps their arms around themselves — increases cortisol, a stress hormone. 

Interestingly, Harvard professor Amy Cuddy and colleagues have found that the relationship works the other way, too. Striking a "power pose" can make you feel more confident in the moment.

A 'cluster' of gestures shows a real feeling of connection

Attraction isn't communicated through one signal but a sequence.

Neuropsychologist Marsha Lucas has a good one to watch for: "After making eye contact, she looks down a bit, gathers or otherwise preens her hair, and then looks up at you while her chin is tipped."

^{Flickr/Art Comments}

Out of 2,000 negotiations videotaped by Gerard I. Nierenberg and Henry H. Calero, the authors of "How to Read a Person Like a Book," there wasn't a single settlement when one of the negotiators had their legs crossed. 

"Psychologically, crossed legs signal that a person is mentally, emotionally, and physically closed off," writes psychologist Travis Bradberry — which may mean they're less likely to budge in a negotiation.

A clenched jaw, tightened neck, or furrowed brow shows stress

All these are "limbic responses" associated with the limbic system in the brain. 

"Emotion, spotting and reacting to threats, as well as assuring our survival, are all heavy responsibilities of the limbic system," says former FBI counterintelligence agent Joe Navarro.

The bus leaves without us, and we are clenching our jaws, rubbing our necks. We are asked to work another weekend, and the orbits of our eyes narrow as our chin lowers."

Humans have been displaying discomfort this way for millions of years, Navarro says.

^{Flickr/Courtney Carmody}

Navarro told Business Insider that we've evolved to display nervousness without using any words.

Some of the most common manifestations of our anxiety? Touching your face and rubbing the skin on your hands. Both can be soothing behaviors when you're feeling uncomfortable.

"It's hilarious how often we touch ourselves under stress," Navarro said.

If they're laughing with you, they're probably into you

If someone is receptive to your humor, they're likely interested in you.

Evolutionary psychologists say that humor — and positive reception to humor — play a pivotal role in human development. They serve as a way of signaling a desire for a relationship, be it platonic or romantic. 

^{AP Photo/John Bazemore}

Whether they're innate or learned, there are a number of signals and behaviors people use when they feel that they're a leader, or at least are trying to convince you that they are.

They include holding an erect posture, walking purposefully, steepling and palm-down hand gestures, and generally open and expansive body postures. 

A shaking leg signals a shaky inner state

"Your legs are the largest area of your body," University of Massachusetts professor Susan Whitbourne says, "so when they move, it's pretty hard for others not to notice." 

A shaky leg signals anxiety, irritation, or both, she says. 

^{Illusive Photography/Flickr}

Riggio's research suggests that there's a specific type of smile people display when they're trying to act seductive.

He writes in Psychology Today:

"[T]hey typically display positive affect — a slight smile that accompanies direct eye contact, with a slow glance away, but still holding the smile.

"Interestingly, the seductive smile could be accompanied by submissive behavior (tilting the head downward), or dominant behavior — proudly and slowly glancing away."

Read the original article on Tech Insider. Copyright 2016.