In this intriguing short video, CNN's Anderson Cooper asks Senator John McCain (R-AZ) about his former running mate, Sarah Palin - and her recent comments on participating in any possible open nomination process at the Republican convention this summer. At first glance, Senator McCain seems to display nonverbal signals of incredulity/doubt/disbelief - as his right eyebrow and forehead elevate repeatedly while his left side doesn't react much.
Looking more carefully however, we can see where most of the entire left side of the former Presidential candidate's face is mildly (and in some places moderately - such as his forehead) consistently less reactive. Indeed, Mr. McCain's smile is even slightly asymmetric (when he smiles with his right side, the left corner of his mouth droops slightly). These are common manifestations of a peripheral cranial nerve VII palsy (the "Facial Nerve"). When all other possible causes of such palsies are excluded (thus referred to as a "diagnosis of exclusion") - this finding is commonly referred to as "Bell's Palsy". Other video of Senator McCain seems to validate a facial nerve palsy.
Although there are other nonverbal signals displayed by John McCain in this video, the valuable lesson here is - if one doesn't look at the whole face (and body), or bases the body language analysis on too small of a temporal "sample size", an erroneous conclusion often will be made.