Lakers guard Kobe Bryant making a classic display of dominance.

What you say communicates only about half of what people hear.

According to UCLA professor Albert Mehrabian, 55% of the message you convey comes from your body language.

That’s why studying body language has such a long history.

None other than Charles Darwin wrote the first academic investigation into body language, his “The Expression of the Emotions in Man and Animals,” published back in 1872.

Over the past century science has made lots of advances into understanding the many social meanings of body language. Here are 17 of the most useful findings, pulled from Psychology Today, research journals, and a few awesome books.

Max Nisen contributed research to an earlier version of this article.

According to Barbara Pease and Allan Pease, authors of 'The Definitive Book of Body Language,' everybody does the shoulder shrug.

The shrug is a 'good example of a universal gesture that is used to show that a person doesn't know or doesn't understand what you are saying,' they write.

'It's a multiple gesture that has three main parts,' they continue. 'Exposed palms to show nothing is being concealed in the hands, hunched shoulders to protect the throat from attack, and raised brow, which is a universal, submissive greeting.'

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 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.'

Making a genuine smile -- also known as a Duchenne smile -- is nearly impossible to do on command. It's why family photos tend to look so awkward.

The smile, it turns out, is 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.

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.

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.'

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.

When you look at 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.'

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.

They may also stand very still and not blink.

How people hold themselves is a big clue as to how they're feeling. Harvard professor Amy Cuddy finds that expansive poses increase testosterone and confidence. If they're leaning back and relaxed, they feel powerful and in control. Similarly, research shows 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.

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 -- which may mean they're less likely to budge in a negotiation.

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.'

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

Evolutionary psychologists say that humour plays a pivotal role in human development. It serves as a way of signaling a desire for a relationship, be it platonic or romantic.

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.

Whether they're innate or learned, there are a number of signals and behaviours 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.

'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.

It's easy to seize on body-language cues, but it's important to be aware of the context. While crossed arms typically indicate that someone is closed off, people are also more likely to cross their arms when it's cold and when their chair doesn't have an armrest.

Be aware of the environment before making a decision or changing strategy based on these types of behaviours.

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