For the record, they ask commonly known questions;...ie age, name marital status, not to put them at ease, but to get a base line reading on your heart and sweat rates. once established they can ask unknown questions and from the deviation from the normal readings would indicate truthfulness or non truthfulness.
A fact, if you put a tack right under your big toe, and press it when you answer every question, you can negate the polygraph and make it totally worthless. The fact that he passed it means nothing.