A young man is sitting by the road eating something. A policeman is coming over. At once ,the man gets up quickly and runs down the road. The policeman runs after him. The man runs very fast. But the policeman runs faster. After a few minutes, the policeman catches him. 'Where are you going?' says the policeman. 'You must be a criminal   if you run like that when you see a policeman.' 'No, no,' says the man, 'I'm not a criminal. I'm just too fat, you see. The doctor says to me that I must always run fast after eating.' 'I see,' says the policeman, 'You are running to help to lose some weight  .' Why does the young man run?
Because the doctor tells him to run after eating. He wants to catch a bus. He sees a friend. He remembers something.