A deterrent to book theft.

The library of the monastery of San Pedro in Barcelona (as recorded in Manguel, p. 244) was inscribed with the following cautionary words:

“For him that steals, or borrows and returns not, a book from its owner, let it change into a serpent in his hand and rend him. Let him be struck with palsy, and all his members blasted. Let him languish in pain crying aloud for mercy…. Let bookworms gnaw at his entrails in token of the Worm that dieth not. And when at last he goes to his final punishment, let the flames of Hell consume him forever.”

"On Stealing Books", by Ben Myers (Faith and Theology).