If you tell about something that was supposed to be a secret, we say you let the cat out of the bag.

VOA: special.2009.09.27

And then he says to Franny: "I'll tell you a terrible secret. Are you listening to me?

然后他对弗兰尼说：,我告诉你一个很可怕的秘密，你在听吗？

耶鲁公开课 - 1945年后的美国小说课程节选

And then he says to Franny: "I'll tell you a terrible secret. Are you listening to me?

然后他对弗兰尼说：,我告诉你一个很可怕的秘密，你在听吗？

耶鲁公开课 - 1945年后的美国小说课程节选