In Eats Shoots and Leaves what analogy does the author say that grammarians use for relationship of punctuation to words?

In "Eats, Shoots & Leaves", Lynne Truss compares the relationship between punctuation and words to the relationship between a conductor and an orchestra.

She argues that just as a conductor guides the musicians to create beautiful and harmonious music, punctuation guides the reader through the words to create a clear and meaningful understanding of the text.