'Matlock' vs 'Human Lie Detector' Episode 3 — Will She Be Found Out?

Weird scene, why is the human lie detector staring intensely at people, telling them exactly what she’s noticing? Wouldn’t it be more effective to simply observe? When she asked “Why are you nervous?” Matty could have truthfully answered “Because you make me very uncomfortable”.And why is Matty as a supposedly skilled liar acting like that? It couldn’t be more obvious that she has something to hide when she literally hides behind other people and is a nervous wreck.