Robot

A family of 3 members included father, mother and a son. One day father decided to buy a robot. The robot had a special quality of detecting someone telling a lie and spank them on the face if they lie. One fine day, the son came home late in the evening. While having dinner, father wanted to enquire upon son's delay.
Father: "why were you late son?"
Son: "Dad I had an extra class in the school?"
Robot slaps the son (as he was telling a lie)
Son: "Sorry dad, I went to theater to watch movie " paranormal activity"
Father: "At your age, we use to work hard in school. We never went to movies like you did. Movies like paranormal activity is not appropriate for your age."
Robot slaps the father.
Mother was overhearing the conversation. She says: " after all, he is your son."
Robot slaps the mother.