" If you have reason to suspect that a person is telling you a lie, look as though you believed every world he said. This will give him courage to go on; he will become 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 at though you did not believe him, this opposition on you part will provoke him into leading out his reserve of truth and bringing the whole force of it to bear upon your incredulity. "

― Arthur Schopenhauer , Essays of Schopenhauer