TheXcitizen

Eyes that lie
Most of us probably grew up hearing, “Look me in the eye when you talk to me!” Our parents were operating under the assumption that it’s tough to hold someone’s gaze when you’re lying to them, and they were right to an extent. But that’s such common knowledge that people will often deliberately hold eye contact in an attempt to cover up the fact that they’re lying. The problem is that most of them overcompensate and hold eye contact to the point that it feels uncomfortable. On average, Americans hold eye contact for seven to ten seconds, longer when we’re listening than when we’re talking. If you’re talking with someone whose stare is making you squirm especially if they’re very still and unblinking something is up and they might be lying you.

Real smiles crinkle the eyes.
When it comes to smiling, the mouth can lie but the eyes can’t. Genuine smiles reach the eyes, crinkling the skin to create crow’s feet around them. People often smile to hide what they’re really thinking and feeling, so the next time you want to know if someone’s smile is genuine, look for crinkles at the corners of their eyes. If they aren’t there, that smile is hiding something.

If their Voice goes up or down, they're most 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."
A clenched jaw signals stress
A clenched jaw, a tightened neck, or a furrowed brow are all signs of stress. Regardless of what the person is saying, these are signs of considerable discomfort. The conversation might be delving into something they’re anxious about, or their mind might be elsewhere and they’re focusing on the thing that’s stressing them out. The key is to watch for that mismatch between what the person says and what their tense body language is telling you.

Crossed arms and legs signal resistance to your ideas 
Crossed arms and legs are physical barriers that suggest the other person is not open to what you’re saying. Even if they’re smiling and engaged in a pleasant conversation, their body language tells the story. Gerard I. Nierenberg and Henry H. Calero videotaped more than 2,000 negotiations for a book they wrote on reading body language, and not a single one ended in an agreement when one of the parties had their legs crossed while negotiating. Psychologically, crossed legs or arms signal that a person is mentally, emotionally, and physically blocked off from what’s in front of them. It’s not intentional, which is why it’s so revealing.

An expansive pose signals power and a sense of achievement
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.

If they mirror your body language, the conversation is likely going well 
When two people are getting along and feeling a connection, their postures and movements mirror each other's.