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The examiner will review every question before you are hooked up. He/she will allow you to answer and explain why you would answer "yes" to this question. Even though you explain yourself, you may still react to this question because I'm sure it evokes an unpleasant childhood memory for you. Polygraphs do not detect lies, they can only gauge emotions which may not have anything to do with being deceptive. Polygraphs are not accurate or reliable. I would urge you to download and read TLBLTD, available free on this site. No one should submit to this so-called testing procedure without knowing what it's really all about.
Accidentally coming across child porn when you were 13 years old and being taken advantage of by a pedophile who showed you child porn during your childhood would not be held against you.