These are some good points. However, it would be a mistake to ignore behaviour. This is because the autonomous nervous system is largely involuntary. It's why we can breathe, our hearts beat and our glands perspire without our thinking about it.
The polygraph (lie detector) works on the principle we have no control over the ANS. Thus, no matter how cool headed you are, or rationally minded, lying is physiologically stressful, causing the damp from the increased perspiration, to cause the galvanometer swing above base rate.
Police and border control officers look out for signs of overly nervous reactions, for example excess sweating, the fight or flight syndrome caused by the adrenal glands kicking out cortisol, adrenaline and noradrenaline, which can cause trembling, the desire to run, fainting, vomiting, pallor, need to defaecate, etc.
It is known criminals are sometimes on a high after a crime. Of course, you will spot it.
Giobbi was a high ranking senior cop who recognises inappropriate behaviour. Amanda flirting with him was a bizarrely callous response whilst on the threshold of the murder scene.