Have you ever bought a used book and found anything inside of it? I have bought used books and found receipts in them from when the book was bought. One time there was a receipt from an airport, so I guess someone bought the book to read on a flight. I have a friend who once bought a western book at a garage sale and found $20 inside. My sister once found some uncashed checks in a book at a garage sale. She happened to see the checks before she paid for the book, so she gave them to the woman who was having the sale. The woman told her that the checks belonged to her son and they were from people who had given him a check for a graduation present. He had put them in the book and then forgot where he had put them. The checks were several years old, so they had been lost for a long time.