A man buys a "lie detector" robot that slaps people who lie. He decides to test it out at dinner.

DAD: Son, where were you today during school hours?
SON: At school. [Robot slaps the son]
SON: OK,I went to the movies.
DAD: Which one?
SON: Toy Story. [Robot slaps the son again]
SON: OK, it was Day with a Porn Star.
DAD: WHAT? When I was your age I didn’t even know what porn was! [Robot slaps Dad]
MOM: HAHA! After all he’s your son. [Robot slaps the mom]