How we change what others think, feel, believe and do
'Tells' are typically small fragments of body language associated with particular habits and behaviors. They are often also associated with one person only.
Tells are triggered by emotions such as excitement, anxiety and anger.
They are often subconscious and thus are useful signals of what the person is really thinking.
They may be very visible actions, such as scratching and vocalizing, or may be fleeting micro-movements, such as twitches of facial muscles.
A poker player scratches his ear when he has a good hand and rubs his nose when he has a bad hand. He is also surprised when some people seem to be able to tell whether he has a good or bad hand.
A child has a tell of scratching his leg when he tells a lie. His mother spots this and uses it to wean him into being more truthful.
A business leader briefly flares her nose when irritated. Some of her people spot this and are careful when it happens.
We do not all have the same body language, although much is shared. This means that reading the signals that other send is not as easy as it may first seem. It thus gives importance calibrating a person before making assumptions. It also means that people will often give you extra information beyond common body language, particularly in individual situations.
As with other body language, tells are typically at transitions, when a person first feels anxious, excited, etc. They do not always persist and can be momentary. This makes spotting them a quite skilled activity. The good news is that people will repeat the tells in a habitual way and, with observation, you can acquire the needed skills.