Deceptive body language
When a person is seeking to trick or deceive you, they there are many different body signal they may use.
Language of deception
A deceptive body is concerned about being found out -- and this concern may show.
Anxiety
A deceptive person is typically anxious that they might be found out (unless they are psychopathic or good at acting), so they may send signals of tension. This may include sweating, sudden movements, minor twitches of muscles (especially around the mouth and eyes), changes in voice tone and speed.
Many of us have hidden anxiety signals. For example: Biting the inside of the mouth (George W. Bush), patting head (Prince William), hands in pockets (Tony Blair).
These signals are almost impossible to stop as we start them very young.
Control
In order to avoid being caught, there may be various signs of over-control. For example, there may be signs of attempted friendly body language, such as forced smiles (mouth smiles but eyes do not), jerky movements and clumsiness or oscillation between open body language and defensive body language.
The person may also try to hold their body still, to avoid tell-tale signals. For example they may hold their arms in or put their hands in their pockets.
Distracted
A person who is trying to deceive needs to think more about what they are doing, so they may drift off or pause as they think about what to say or hesitate during speech.
They may also be distracted by the need to cover up. Thus their natural timing may go astray and they may over- or under-react to events.
Anxiety may be displaced into actions such as fidgeting, moving around the place or paying attention to unusual places.
Reasons for deception
There can be many good reasons for deception.
Persuading
Deception may be an act that is intended to get another person to say or do something.
Avoiding detection
Deception also may be more self-oriented, where the sole goal is to get away with something, perhaps by avoiding answering incriminating questions.
Source: changingminds.org