"If you have nothing to hide...."
It's for The Children.
The so called trick to polygraphs is to train yourself to answer a different question than the guy asked. For example
Tester: Did you kill your wife.
You(thiniking in your mind): Am I a billionare?
You(outloud): No
Supposedly if you do it right you can train yourself to do it fast enough to get a false positive or atleast a undeterminable result.