liars try to exaggerate emotion so they wont be suspected of lying. 🤐
You may also catch a liar by the attempt to maintain eye contact since some may believe the myth that liars avoid eye contact. There may also be a number of physiological responses that aren't indicative of lies precisely but by the stress that lying often involves. However, many of these signs may vanish when you're dealing with pathological and experienced liars.
The aim in lie detection is to pick up on the subtle physiological responses, whilst understanding that you're observing stress not a lie. So interrogation techniques involve observing a stress indicator during the course of the interaction, noting at what point that sign revealed itself and then returning later to discuss the same topic and watching to see whether the sign reappears.
Another important facet is getting a baseline read. Someone who is always shifting uncomfortably, may be read as lying without understanding this baseline behaviour. The baseline is the normal set of traits, behaviours for the individual.