The term "mirroring" is used to describe the practice of copying the behavour of the person you are interacting with. It is well established that mirroring can created a sense of connectedness between yourself and the other person.

You can use this factoid in two ways. Firstly, if you want the other person to feel at ease and connected with you, you can deliberately mirror their behaviour. So for example if they cross their arms then casually, in a moment or two, you cross your arms. If they put their hand to their face, you do the same. It is quite uncanny how comfortable this makes people feel.

Secondly, you can observe them. If they are mirroring you they are feeling connected and warm towards you. (unless they are trying the experiment on you at the same time of course)

Think this is just pyschological hocus pocus? Well researchers in Holland have found that waitresses that mirror the customers they are serving receive, on average, almost double the tip.