I saw a funny scene in a movie today.  Most that saw it probably did not even think about it.  The police hooked up a psychopath to a lie detector to see if she was telling the truth.  - Eh.

As I stated before in a previous post about Caylee Anthony:

• More appropriate details provided by psychopathic offenders compared to nonpsychopathic offenders when lying (but no difference when telling the truth)
• No difference in narrative length between the true and false conditions among psychopathic offenders, and for both groups, truthful narratives were longer than false narratives
• For psychopathic offenders, spontaneous corrections more frequent when lying compared to telling the truth. This is opposite to the finding with non-criminal populations - according to CBCA, the presence of spontaneous corrections is thought to be associated with credibility.
• Psychopathic offenders judged less credible than non-psychopathic offenders, even when telling the truth. Seven times less likely to be judged credible to be precise.
• Narratives produced by psychopathic offenders were judged to be less coherent overall than narratives produced by non-psychopathic offenders. 

Um - you know the real problem is that a psychpath does not see the difference between truth and what he or she wants to be the truth. So there is nothing to detect.  Then again, lie detectors don't work and the psuedo-science which is closer to voodoo than it is science known as polygraph testing is not reliable at all.