One boy was riding a cycle on road at night. A policeman stops the boy in the middle of the road and questions him.
Policeman: "Why have you not switched on the lights in your cycle?"
Boy: Police Uncle, there are lights on every street. So why should I turn on the lights.
To this the Policeman removes the air from his bicycle’s tyre.
Boy: Why are you removing the air from the tyre?
Policeman: Don’t you know air is everywhere!