my belief is that you simply can't ...
you can tell when he's lying with body language.
Answers.com says to Try a truth serum: (based on: http://www.answers.com/topic/truth-drug?cat=health )
Drugs...
The truth is in the details. When he (or she) includes numerous unrelated, small details that don't add any extra "luster" or "sparkle" to the story you're being told (remember, his story is being...
Almost everyone lies occasionally. Usually for a reason: too keep from hurting someone's feeling, to stay out of trouble, to keep from being embarassed or the like. Most people only lie when they...