Crack是“裂缝、断裂”，这个短语是什么意思呢？请看对话：

    A: What’s so funny that you are watching?

    B: I’m watching the Conan show. That comedian really knows how to crack up an audience.

    Note: “Crack” can mean “to make a sharp sound” and “to break without dividing into separate parts,” as in “to crack a nut.” There is also the informal use of “cracking a joke,” meaning “to tell a joke.” This idiom means “to make someone laugh very hard, to make someone break out laughing.” It’s said that the expression comes from Gaelic, in which the word “craic,” pronounced crack, refers to fun. For example: You and your jokes really crack me up.