They both tell the truth except for the days when they tell a lie?

I'm not sure that is true actually. Anyone can laugh and lie, they can do it to wind you up or play you for a fool to your face.

yes because it would tell the truth if a guy is lieing ** NEW ANSWER ** A polygraph instrument is a machine and can not tell the truth or tell a lie. In the hands of an experienced examiner, the...

Pablo Picasso

You can't all you can do is trust or not trust

That's confusing. Well, if he ALWAYS lies, and he said that he lied, would mean he had told the truth though he could have lied so the situation may be a lie