George came home from University in tears.
"Mom, am I adopted?"
"No of course not!", replied his mother. "Why would you think such a thing?"
George showed her his genealogy DNA test results. No match for any of his relatives, and strong matches for a family who lived the other side of the city.
Perturbed, his mother called her husband. "Honey, George has done a DNA test, and... and... I don't know how to say this... he may not be our son."
"Well, obviously!" he replied.
"What do you mean?" she asked.
"It was your idea in the first place" her husband said. "You remember, that first night in hospital when the baby did nothing but scream and cry and scream and cry. On and on. And you asked me to change him."
"I picked a good one I reckon. Ever so proud of George."
As the nurse is making the rounds at the old folks home... She stops by Carl's room and sees him putting black shoe polish all over his penis. Dismayed, she exclaims "no, no, no Carl, you misunderstood. I said remember to turn your clock back."