A Man & a lie detector

A man bought a lie detector robot that slaps the person who lies…
The man decided to try it out at dinner.

Dad: Son, where were you during school hours.

Son: At school.

The robot slaps the son.

Son: Ok! I was at my friend’s house watching a DVD.

Dad: Which one?

Son: Kung Fu Panda

The robot slaps the son again.

Son: Ok! It was an erotic movie.

Dad: What!? When I was your age I didn’t even know what an erotic movie was.

The robot slaps the dad.

Mom: HAHAHAHAHA. He is your son after all!

The robot slaps the mom.