Between the Pages

Yesterday I found this lovely old photograph. It fluttered out from between the pages of a book on women and love. On the back it is a very old "The Season's Greetings" card. They were glued together lord knows how very long ago. Once I found a smooshed complete hummingbird between the pages of a heavy art book.
What is the most interesting thing you ever found between the pages of a book?

original photo above and enhanced photo below