Murmuring.

Until then I had thought each book spoke of the things, human or divine, that lie outside books. Now I realized that not infrequently books speak of books: it is as if they spoke among themselves. In the light of this reflection, the library seemed all the more disturbing to me. It was then the place of a long, centuries-old murmuring, an imperceptible dialogue between one parchment and another.

Thus I rediscovered what writers have always known (and have told us again and again): books always speak of other books, and every story tells a story that has already been told.

Umberto Eco, from the postscript to The Name of the Rose