Cursed cats! They are so fond of disrupting human work, especially medieval manuscript composition. In 1420, a scribe in what is now the Netherlands discovered that a cat had urinated on a page that he had written. He added illustrations of the event and the subsequent damage to the book, as well as provided helpful advice:

Hic non defectus est, sed cattus minxit desuper nocte quadam. Confundatur pessimus cattus qui minxit super librum ostum in nocte Daventrie, et consimiliter omnes alii propter illum. Et cavendum valde ne permittantur libri aperti per noctem uni cattie venire possunt.

When translated into English, that reads:

Here is nothing missing, but a cat urinated on this during a certain night. Cursed be the pesty cat that urinated over this book during the night in Deventer and because of it many others [other cats] too. And beware well not to leave open books at night where cats can come.

Link -via Alexis Madrigal | Photo: Historical Archives of Cologne