Gestures of considering and doubts

Concentration. It is expressed in touching the bridge of the nose with the closed eyes. When the person you are speaking to decides what to do and where to go and considers something he/she usually rubs his/her chin.
Considering. If the person holds the hand near the chin with the stretched index finger along the chicks and another hand holds the elbow and his/her left brow is sank, then you'll understand that he/she got the certain opinion about the situation.
Positivism. People show positivism as the small incline of the head forward and the light touch the chick with the hand. The body is inclined forward. If you noticed such postures and gestures it means that the person is interested in what is going on and his/her attitude is positive.
Distrust. Probably you've noticed that sometimes students close their mouth with their hands listening to the teacher. This gesture means he/she doesn't agree with the opinion of the teacher and what he/she says. They seem to hold their expressions pressing their sincere feelings and worries. If your friend made the gesture of distrust consider your words. This knowledge can be really helpful in talks with the boss.
Uncertainty. Such nonverbal gesture as scratching or rubbing behind the ear or the neck can indicate that the person doesn't realise what you want from him/her and what you meant. But how to react if the person still says he understands you. Just repeat your petition once more. If the hand holds another one by the elbow it also means uncertainty. Probably such person is in badly-known society.