The show 'Lie to Me' is based on the idea of microexpressions, and if you can accurately see and interpret these findings, then you can be a human lie detector.
I seem to have a knack for this, as I am usually pretty good at spotting the liars, the folks who are outright dishonest about their history of medications usually. But they usually make it pretty easy when they tell me they need 6 xanax a day and oxycontin is the only medication that relieves their chronic back pain.
Knowing when someone lies to you is a remarkably depressing experience. It is one thing to be ignorant of what someone is doing, but to see the lies, that hurts. Still, one thing that people really have a hard time with is the manipulative patient who is actually in pain. I know that he's mean and demanding and wants dilaudid 4mg IV q2 hr, but he is s/p fasciotomy for necrotizing fasciitis. I think he deserves some pain medication, even if he is a jerk.