Lie Detector

A father buys a Lie Detector Robot that slaps you when you lie. All excited, he decides to test it out on his son at supper.
"Where were you last night? the father asks.
"I was at the library." Robot slaps the son.
"OK I was at Jimmy's house."
"Doing what?" the father asks.
"Watching a movie.....Toy Story." Robot slaps the son.
"OK it was porn!" cries the son.
Father yells "What? When I was your age I didn't even know what porn was."
Robot slaps the father.
The mother laughs, "He certainly is your son!"
Robot slaps the mother.