There are 2 different approaches for each sexes.
For Males OBSERVATIONS
the eyes deviate slightly to the left indicating the Male is accessing the creative part of the brain
heartrate elevates in an attempt to support the strain of the creative effort
pupils constrict slightly instinctively in preparation for flight/fight response
sweatpores extend slightly to reduce heat and give the appearance of being cool CONCLUSION If all these match then the subject has a high probability of having lied in response to the question
For Females OBSERVATIONS
is she breathing?
is her mouth open and words are coming out of them? CONCLUSION she’s lying
Edit: sorry this came from a bad place. Just had an 8 year relationship break