A dad buys a lie detector robot that slaps you if you lie.
Dad: Son, where were you at school hours?
Son: At school. The robot slaps the son.
Son: Okay I was watching KungFu Panda! The robot slaps his son again.
Son: Okay I was watching violent movies!
Dad: What?! When I was your age I never watched those kinds of movies! The robot slaps the dad.
Mom: Haha, after all, he is your son. The robot slaps the mom...