But remember it is observing everything not just one thing and you do have to catch it at the time because you wont get another chance.
A liar might rub his nose, divert his look elsewhere, and say after deliberating it over in his mind something like: "I did not take the money!".
Liars generally stress each word and use words together like "I" "did" "not".
A person that is innocent would likely use words like: "I didn't".
And also when someone is GUILTY they will say things like: "I did not do it!" I am not guilty!". "I was not even in the xxxx when it went missing!" and get on the defensive. Very angry and hostile. On the defensive is what you need to take into consideration.
What a blinkin walk down memory lane. WOW!
DND