这个短语的字面解释是“口吐白沫”，这是什么意思？请看对话：

    A: Did Mary get her car fixed?

    B: Yes, but she was almost foaming at the mouth when she heard about the cost.

    Note: The idiom means to “be enraged and show it.” Dogs and other animals affected by rabies foam at the mouth. There are examples of forms of this phrase in old and middle English that date back to at least the first millennium. The Lindisfarne Gospels, 950, have a reference to “spumat faeme.” The earliest version in a form that we can now readily understand is in Shakespeare’s “Julius Caesar,” 1601: He [Caesar] fell down in the marketplace, and foamed at mouth, and was speechless.