It was already dark when an old man came to a small town. He found an inn and wanted to stay there for the night. After he had gone to his room, the owner said to his wife, "Look at his bag, dear. I'm sure there are lots of valuable things in it. I want to steal it when he is asleep." "No, no," said the woman. "He must look for his bag tomorrow morning. Then he'll take you before the judge." They thought and at last the woman had an idea. "We have forgetful grass," said the woman, "Why not put some into his food? If he has the food, he will forget to take his bag away." "How clever you are!" said the owner, "Don't forget it when you prepare supper for him." The old man had the food with the forgetful grass and went to bed. The next morning, when the owner got up, he found the door was open and the old man had left with his bag. He woke his wife up and said angrily, "What a fool! Your forgetful grass isn't useful at all." "No, no," said the woman. "I don't think so. He must forget something." "Oh, I've remembered!" The owner cried out suddenly, "He forgot..." The owner and his wife put the forgetful grass into the food because   _  .
the old man always forgot something they wanted to make the food better they hoped the old man would leave the bag in the inn they wanted to know if the grass was useful