What is the cheesiest book you’ve ever read? For Washington DC librarian Anna Holmes, it wasn’t so much the book, as the slice of Kraft American that she found inside it, clearly used by a cheese-loving patron as a bookmark. The library branch has seen three “cheese bookmark” incidents to date, according to Holmes, who made a plea on Twitter for readers to “PLEASE stop using cheese as a bookmark. Please. We give away actual bookmarks for free. Or like use a receipt or something. Just not perishables.”

Whiffy as that sounds, that trio of dairy product delinquents are not the worst offenders, librarians across the world have revealed in response to Holmes’s plea. There are those who use banana skins, broccoli (“It was cooked and buttered well. I think the greasy stain made it easy for them to find their page”), cooked bacon and a fried chicken leg. Inedible but equally jarring fold-ins reported included Lego, flowers, money, a used condom, and a sawblade.

Bacon, it turns out, appears to be a bit of a thing, with librarians previously reporting the discovery of surprise rashers all over the place. In his Salt Lake City branch, Josh Hanagarne also discovered “a lock of hair, like, the size a serial killer would take from a victim”, and “a Polaroid of a cat wearing a leather mask”.

Conducting this important research also brought me to Forgotten Bookmarks, a gift of a website where used bookseller Michael Popek charts the things he finds inside the antiquarian books he buys. Some of the best include a marriage certificate dated 18 October 1899, found in an 1850 copy of the Bible, and a recipe for cheese souffle, found in Charles Darwin: Evolution and Natural Selection. But Popek’s site itself is a charming and moving glimpse into other people’s reading lives – the advertisement for a roach exterminator found in Backgrounds of American Literary Thought; the family photographs left behind by previous readers; the small and intriguing key found in Ocean Grove Christian Songs. Who were these readers, what did they think of these books, where are they now?

As for me, I am an unabashed page turner-downer and spine-cracker of the books I own, to the horror of my husband. It’s sacrilege to many, but although I love my books, I don’t mind that they look read. And reread. And reread. They are not decoration.

Library books, though – I wouldn’t dare. Receipts, hairbands, leaves – I’ve roped them all in. Never food, though. Never bacon. As Tom Clayton at Melville House ponders, how on earth does this scenario come about? “You’re halfway through breakfast … And you’re enjoying your library book, too. But! Then! The phone rings in the other room. You ignore it. It rings again. And again. It must be urgent. There’s only one logical thing to do in this situation: pop some bacon in your book.” Or maybe not.