Look for a lack of crinkles around the eyes to detect a fake smile.
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 wont see the wrinkles.
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.
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."
If they mirror your body language, the conversation is probably going well.
When two people are getting along, their postures and movements will mirror one another. 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" one another when we're feeling a connection, says positive psychologist Barbara Fredrickson.
Eye contact shows interest — both positive and negative.
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."
But if they look into your eyes for too long, they might be lying.
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.
An expansive pose signals power and a sense of achievement.
How someone holds themself is a big clue 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.
Crossed legs are usually a sign of resistance and low receptivity, and are a bad sign in a negotiation.
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.
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."
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 plays a pivotal role in human development. It serves as a way of signaling a desire for a relationship, be it platonic or romantic.
A clenched jaw, tightened neck, or furrowed brow shows stress.
All of 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," explains 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.
Expansive, authoritative postures show leadership.
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.
Crossed arms can signal defensiveness, depending on the context.
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 behaviors.