Among the photos taken at the "chained library" of Zutphen is the one embedded above (cropped for emphasis), depicting the prints of animals in the floor tiles. Local folklore calls these "The Devil's Footprints":
In the floor under the reading desks we can see tracks made by the Devil. According to a poem by the 19th century poet A.C.W. Staring, the Devil caught the monk Jaromir eating a chicken in the ‘Librije’ during Lent! The Devil punished Jaromir by locking him up in the ‘Librije’ for one night.Reader Gelvan Tullibole 3rd offers an alternative interpretation:
We have seen footprints in clay roof tiles in Central France. At first we had visions of a cat or dog running over the wet tiles but no. Animal footprints were added to every firing to protect it from shattering or not cooking properly. These tiles are considered lucky and it is unlucky not to have at least one in the roof.I would bet the "intentional" and "lucky" aspects of the French interpretation were devised by the local potters eager to sell their wares but unable to keep small mammals out of the clayworks.