You may notice other peoples body language and have already decided what they are thinking or feeling. Our past experiences tell us what to look for and we can make the behaviour fit our expectation.
If a group of people were shown the same picture it is likely that they would all see something different in it, their description might not sound like the same picture. This is because we all look through our own filter of the world. In other words the information that is important to you is what you will see. The same applies to body language, we focus in on what is familiar or important to us. Noticing our own perception of another’s body language is vital when changing patterns of behaviour. Once you are aware of your perceptions, then rather than reacting to it (same old pattern) you can check it out with the other person in the kindness way possible.