When the therapist grasps the chair arm Lightman interprets it as sign that she agrees that Samantha was abused. It could also be an attempt not to lose control of herself, or what she is willing to reveal.
Lightman talks angrily on the phone to his daughter so Foster can check how Samantha’s parents react: their sympathy, then horror is not what you would expect from abusive parents. Lightman used this same trick in earlier programs – seeing how people react to something he does just to see how they react. Without words the listener’s facial expressions provide useful information. Much later in the program Lightman finds out where the other girl is hidden even though Samantha won’t tell him. Her nonverbal reactions to his twenty questions game give it away.
Sweating & Swallowing
Profuse sweating when someone is not engaged in effortful activity is usually a sign of strong emotional arousal. A few minutes later Lightman comments on how Samantha’s repeated swallowing also shows strong emotional arousal. Both sweating and swallowing are driven by the same mechanism.
Battered Person Syndrome
The detective asks Lightman if Samantha has “Stockholm syndrome”. That phrase refers to hostage or kidnap victims identifying with and wanting to protect the person who captured them. Foster says Samantha more likely has battered person syndrome.