Foster calls Jenkins a pathological liar; and so does Lightman later in the program. I think the portrayal of Jenkins better fits a sociopath: anti-social, manipulative and exploitive of others for his own entertainment, and charmingly socially skilled. Sociopaths only lie when it suits their purposes, they are not compelled to lie. Just such a compulsion reputedly is what characterizes pathological liars, who are said to lie even when the target knows they are lying, even when they don’t benefit from the lie. I have examined a few people who claimed to be pathological liars but I was not convinced they had no choice. I doubt there really are such people.
Jenkins cleverly lies about everything to prevent the establishment of a baseline — a standard of what he is like when he is truthful. Changes from the baseline are crucial for spotting lies. Jenkins knows this and that is why early in the program he never tells the truth; it is not that he is compelled to lie, he chooses to lie to defeat Lightman’s team.
The prison guard’s nostril flair could be a sign of fear, but it also occurs with anger and sadness. The only way to tell which emotion it is would be by the expression on the face, but the actor playing the guard doesn’t show an expression of any emotion that I could see when he flared his nostrils.
Looking down and away can be a sign of shame but it also occurs in disgust. Which it is could be revealed by the facial expressions but the guard again doesn’t show much.
Anger can come on slowly, but sometimes genuine anger can be abrupt; it depends on the person and the circumstance. But false anger often has a jagged or stepped, rather than smooth onset onto the face.