Lightman is using the guilty knowledge technique, mentioning something that only the guilty not an innocent person will know about and watching for who shows a reaction. This technique is sometimes used in polygraph exams: ‘was the person strangled, shot, stabbed, bludgeoned to death?’ Only the killer knows and is likely to show a physiological reaction when the actual weapon is mentioned. Often the newspapers reveal so much about a crime that this technique can’t be used because everyone knows everything the police know.
Lightman acknowledges that he can be fooled. When we measured every behavior we could see or hear there were still a few people we could not classify as either liars or truth tellers – they are what I call natural performers. They don’t lie more often than other people, but you can’t tell when they do.
Torres tells Lightman that because of his friendship he is off his game. She is right; when we have a stake in a relationship we are blind to signs of deceit. We don’t want to know truths that would challenge or destroy a cherished relationship.
Bite Your Lips
Lip biting in response to critical questions suggests an increase in stress. It could be generated by the fear of being caught or the fear of being disbelieved. It is a hot spot marking the need for Lightman to find out why it occurred.