Lightman says he needs to establish a baseline to know what these guys look like when they are not stressed. The term baseline refers to a person’s usual behavior during ordinary circumstances. Changes from that baseline suggest that something important is occurring: it might be the stress of being under suspicion or emotional reactions to telling a lie. Without a baseline we run the risk of misinterpreting unusual behaviors, for we don’t know if the person always acts in that unusual way. It is risky to judge truthfulness without a baseline; hence my practice of never making an important decision based on a single, brief meeting.
Antoine is clenching his teeth, which is a nervous habit in some people, but when it is not (which you would know if you had a baseline), teeth clenching suggests an attempt to tightly control what is said or shown.
Lightman and Foster argue about an ethical dilemma: is it justifiable to sacrifice the future of an innocent person (Andre) to prevent many people losing their lives. Factors to consider are: a certainty (with Andre going to jail) as compared to a possibility of a terrorist attack that cannot be stopped by any other means; jail (Andre) versus death (terrorist); what you do (Lightman) as compared to what others (antiterrorists) may be doing; and whether you can ever accept acquiescing in an injustice.