Hey Pandas, Post The Most Interesting Thing You Have Found In A Book (Closed)

Over the years, I have found some fun and interesting items left behind in books: Old class schedules, pressed flowers, punch cards, etc. What have you found?

#1 The Coolest Advertising Ephemera I Have Ever Seen: Riverside (Ca) County Fair, 1916

#2 This.

#3 In A Dictionary Of The Hmong Language