How we change what others think, feel, believe and do
Chest body language
The chest can send a few non-verbal body language signals.
Pushing the chest forward draws attention to it, and can be a part of a provocative romantic display. Women, especially, know that men are programmed to be aroused by the sight of breasts. When women push forward their chests they may thus be inviting intimate relations (or just teasing). This is a function of high heels, which curves the spine to push out the chest and buttocks.
Men also thrust their chest out to display their strong pectorals (and perhaps hide their bulging gut). Enlarged pectorals are, along with biceps, the most common muscles that are used to assess overall strength.
A difference with men is that they do this both to women ('Look at me - I'm strong and will protect you and our babies') and also other men ('I am strong, so you'd better not get in my way').
When the person stands sideways or at 45 degrees, the effect of a thrust-out chest is exaggerated as the person is seen in profile. Women may use this to display the curve of their breasts. Likewise, men may show their strong profiles.
The chest cavity, although protected to some extent by the ribs, contains vital organs and thus is vulnerable in attack. When the chest is pulled back, this may well indicate that the person is trying to hide or appear inoffensive ('I am weak - please don't hurt me!'). Curling forward the shoulders may offer further protection.
When the upper body leans forward it is moved close to the other person (in particular the head). This can have two meanings. First, it shows interest, which can be a simple interest in what the other person is saying ('I want to hear what you are saying'). It can also show a more romantic interest ('I want to get closer to you').
Secondly, leaning forward can invade the body space of the other person, hence posing a threat ('I can hit you from here'). This is often an aggressive move that appears in dominant body language. It is also a common unconscious pattern of powerful people.
The chest expands and contracts with breath. When the person is breathing deeply, then the chest moves more.
Deep breath may be used to help thrust out the chest, as above. It also increases the oxygen intake and readies the person for action, thus indicating such as fear or anger. We also breath deeply when we are experiencing intense emotions such as love.
A person who is particularly anxious may breathe too fast and deep and so hyperventilate, taking in so much oxygen they get giddy (and can even faint).
When the body is held rigid, then breathing is more difficult and short breaths are more likely and may indicate tension.
When a person in a state of hopeful suspense they may hold their breath, as if breathing would either cause what is feared or destroy what is being enjoyed.
Touching the chest draws further attention to it. When a woman does this in front of a man it makes the man think of doing this and is thus a highly suggestive and flirtatious act.
Rubbing the chest can also be a sign of pain of discomfort, perhaps from tension and stress.