A Father buys a lie detector that makes beep sound when it detects a lie.
His son comes home at the usual time after school. He askes: “So, you were at school today, right?”
Son: “Yeah.”
Detector: “Beep.“
Son: “OK, OK, I was in a cinema.”
Detector: “Beep.”
Son: “Alright, I went for a beer with my friends.”
Father: “What?! At your age, I wouldn’t touch alcohol!“
Detector: “Beep.”
Mother laughs: “Ha ha ha, well, he really is your son!”
Detector: “Beep.”