What to keep track of while talking to fellow humans
So there's people who want to see lies and know when they are betrayed, people who want to empathize with others on a better level and psychopathic social engineers who want to know everything about your behavior to then change it and have fun with you. Anyhow if you want to see whenever people mask something there's plenty - PLENTY - of things you can keep track of. This is gonna be a long list of plain information; enjoy!
The NAS
The NAS - or spelled out Nervousness Activation System - is responsible for making you sweat, increasing your heartbeat and breathrate and increasing your bodies temperature whenever you get emotional. Between some emotions are slight differences in the relation of each symptom however those are neglectable due to individual differences beeing larger.
As you probably know it is impossible to always keep track of all the signals everyone is giving throughout conversations. In face-to-face conversations it might be but not in group conversations. Thus I discovered for myself it works good enough to only pay attention to one's NAS and if it triggers while the conversational partner acts as if there wasn't any emotion. Only when this happens I start to look for deceit or concealment of information, if the topic promotes it (if your friend is playing it nice that he got to do a chore after losing a bet it's not worth confronting deceit).
Breathing
While this is included in the NAS breathing can sometimes give other clues too. When someone makes a statement and awaits your response but is holding his breath then you know it's a critical statement of which he knows there is a thing to that you might not like. For example a car salesman who is about to make a deal but states the last thing about 'the car has a minor problem but its neglectable' holds his breath. Then you as educated behavior analyst would know about his attempt to conceal something.
Besides these there of course are things like increased and lowered breathing rate (=stress/relaxation).
Bodylanguage in general
Bodylanguage is a large field of study so I will not get into detail. If you want to read into it yourself I recommend Joe Navarroe's books. However if you notice bodylanguage incoherence after the NAS activated and notice more than one or two weird aspects then you are onto something. Make sure to talk around the topic a little more and ask yourself whether it would be worth it to confront the person with anything. It's often better to slowly talk into it or ask nicely and with skilled phrasing.
The eyes
Why the hell the eyes as seperate segment - You ask? Well the eyes are most giving. You learn to mask emotions with your mouth, your arms, your body in general but you barely pay attention to masking with your eyes. Especially when it comes to sadness, anger, fear, happiness, ... actually any emotion. While the feet are still the most certain and true part about one's bodylanguage the eyes give the best microexpressions. If you learn to read eyes you learn to read emotions. A small checkup of emotional indicators I always look out for:
Anger: narrowed eyelids
Fear: both eyelids pulled upwards; the lower pupil won't be visible anymore
Sadness: more water in the eyes;lower eyelid raised
Happiness: both eyelids raised; wrinkles around the eye; sometimes more water in the eye
~ztlss
















