There once was a teenager who used his parents' extra car without permission. His mom got home, took one glance at the car, and then grounded the kid because she knew he used it.

Another opportunity came up to use the car. The kid tried to get the car at the exact same spot, but again, he was immediately grounded when his mom got home.

That happened again and again. The kid took polaroids; lining up the car and even the tire tread exactly as shown in the pictures. Still... Grounded.

Years later, after acquiring his own teenager who liked to break the rules, the kid asked his mother how she knew when he'd take the car.

She replied, "Oh that! I would just put a hair in the door. If it was gone I knew you had taken the car. 😁"