lie detector

A man buys a lie detector robot
that slaps people who lie. he
decided to test it at dinner:
Dad: Son where were u today
during school hours?
Son: At school (robot slaps son)
..Son: Okay I went to watch a movie!
Dad: Which one?
Son: Harry Potter (robot slaps him
again!)
Son: Okay I was watching porn.
Dad: What? When I was your age
I didn't even know what porn
was! (robot slaps dad)
Mom: Hahahahaha! after all he is
your son!(robot slaps mom)