Guy: 'Doctor, my girlfriend is pregnant but we always use protection and the condom never broke. How is it possible?' Doctor: 'Let me tell you a story. There was once a hunter who always carried a gun wherever he went. One day he took his umbrella instead of his gun and went out. A lion suddenly jumped in front of him. In order to scare the lion, the hunter used the umbrella like a gun, and shot the lion and killed it!' Guy: 'Nonsense! Someone else must have shot the lion.' Doctor: 'Good! You understood the story. Next patient, please.'