how to detect a lie
Although a person lying to someone else in real life is not exactly the same as an actor not fully entering into the situation of the scene, there are a lot of affinities. Many of the tells outlined in this video also show up in scene work. Notice particularly what he says about the liar placing something between himself and his listener, touching his nose or hair (a big one!), engaging in erratic eye behavior (I wrote about the importance of eye contact here) and producing unnatural speech.