By necessity every book must have at least one flaw; a misprint, a missing page, one imperfection.... the Rabbis... point out that even in the holiest of books, the scroll resting inside the Ark, the Name of Names is inscribed in code so that no one might say it out loud, and chance to pronounce properly the Word that once divided the waters from the waters and the day from the night.... As it is, some books, nearly perfect, are known to become transparent when opened under the influence of the proper constellation, when the full moon rests in place.  Then it is not uncommon for a man to become lost in a single letter, or to hear a voice rise up from the silent page; and then only one imperfect letter, one missing page, can bring him back to the land where a book, once opened, may still be closed, can permit him to pull up the covers around his head and smile once before he falls asleep.
—Midrashim, by Howard Schwartz

I have been a word in a book.
—"The Song of Taliesin" in The Black Book of Caemarthen