While thumbing through the medieval manuscript in July 2011, Emir O. Filipović, a teaching and research assistant at the University of Sarajevo, discovered pages of the book stained with the inky paw prints of a cat and snapped a picture—something he planned on sharing with colleagues and students for a laugh.

"I never could have imagined the attention that those prints would subsequently receive," Filipović wrote in an email.

Filipović sent the photo to fellow historian Erik Kwakkel via Twitter in September 2012, but it wasn't until earlier this year that the paw prints saw a flurry of reblogging, retweeting, and sharing.

"It's not very often that a researcher can come across curious things while sifting through monotonous and dull archival