One day, I happened to meet an Englishman in the street and soon we began to talk. As I was talking about how I was studying English, the foreigner seemed to be very surprised, gently shaking his head and saying, “You don't say ! ” I was puzzled( 困惑的 ) , and I thought , “Perhaps this is not a right thing to talk about.” So I said to him, “Well, shall we talk about the Great Wall? Have you ever been there ? ” “Certainly! Everyone back home will laugh at me if I leave here without seeing it. The Great Wall is wonderful ! ”“Yes, it is one of the wonders in the world. And people of many countries have come to visit it.”As I went on telling him more about it, he stopped me again, “You don't say ! ” I couldn't help asking, “Why do you ask me not to talk about it ? ” “Well, I didn't ask you to do so , ” he answered, greatly surprised. “Didn't you say ‘You don't say ! ’ ? ”I asked again. Hearing this, the foreigner laughed loudly. He began to explain, “‘You don't say ! ’ means ‘Really’. Perhaps you know little about English idioms( 惯用语 ) . ” Wow! How foolish I was! Since then I have been careful with English idioms.