According to the FBI's "Reading People" book by Joe Navarro, in psychology, pursed lips seem to be telling the limbic system of the brain to keep our mouths shut and not let anything in. Pursed lips can be a sign that something is wrong or that a person is having a problem. But even though pursed lips are a negative expression, it doesn't mean that the person who purses their lips is lying. They're just stressed.
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