1. Voice changes
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Changes in a person’s normal behavior can betray discomfort of some sort, and might be a tip-off to lies. These departures from normal behavior are most useful when you are observing someone you know well and are familiar with their normal patterns and departures from those patterns.
If you don’t know your subject well, spend time paying attention to how she or he normally talks and acts when relaxed. Is her speech normally slow or quick, loud or soft? What is the quality of his voice usually like? Then, watch for distinct, but not subtle, changes from the normal pattern, retired FBI criminal profiler Gregg McCrary tells Real Simple.