I found this in the Feehan Memorial Library at the University of St. Mary of the Lake/Mundelein Seminary. I like it so much I copied it down:
A Curse Against Book Stealers
For him that stealeth a book from this library,
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,
and let there be no surcease to his agony
till he sink to dissolution.
Let bookworms gnaw his entrails in token of the worm that dieth not,
and when at last he goeth to his final punishment,
let the flames of Hell consume him for ever and aye.
-From the monastery of San Pedro, Barcelona