They'll keep modifying the question and will act more and more outraged and angry until they can intimidate you into issuing a denial.

For instance, if the control question is "have you ever broken any traffic law ever?" and you're honest (which is, despite what polygrapher's say, a good trait to have) you'll say "yes" (unless you don't drive, in which case they wouldn't have asked that question).  The polygrapher will ask for specifics (which they'll probably already have, if this is a pre-employment test; they'll have checked out your motor vehicle records already).

The polygrapher will then ask the question again, adding "Besides what you have told me, have you ever broken any traffic law ever?"  He will also act disappointed in you and outraged that you are such a evil thing as to have run a red light.  Shaking his head, he'll explain that running red lights correlates closely with committing treason (if a pre-employment exam) or with committing whatever crime or act is being investigated.  This is, of course, nonsense.

If you make further admissions, he'll act even more upset and will ham it up all sorts of ways until he can, finally, get some sort of statement that you can deny: "Besides the 78 times you've told me you've broken a traffic law, and with the knowledge that if you have committed a 79th offense I will shot you dead where you sit, have you ever committed any traffic offenses?"

If you refuse to lie, you're refusing to be tested, so far as polygraphers are concerned (I believe former APA president Skip Webb said that.  He also said that, if true that George Washington "couldn't tell a lie", he couldn't be polygraphed either.  The toothless bastard.)

I meant to say  what if"...probable lie questions truthfully.."

What if you always answer the truth to the control questions during a probable lie test. ie... if asked have you ever cheated in school-- or if you've ever lied to a loved one---you just keep answering yes even if they modify the question?