Section 41 If You Have Reason to Suspect That a Person Is Telling You
a lie, look as though you believed every word he said. This will give him courage to go on; he will become more vehement in his assertions, and in the end betray himself.
Again, if you perceive that a person is trying to conceal something from you, but with only partial success, look as though you did not believe him, This opposition on your part will provoke him into leading out his reserve of truth and bringing the whole force of it to bear upon your incredulity.