Yesterday I found the above picture via twitter and then this article:
"Everyone who has ever owned a cat will be familiar with their unmannerly feline habit of walking across your keyboard while you are typing. One of the manuscript pictures tweeted by @erik_kwakkel (http://twitter.com/erik_kwakkel/status/
The marks of cat paws were neat but my favourite mention of cat on manuscript is:
"A Deventer scribe, writing around 1420, found his manuscript ruined by a urine stain left there by a cat the night before. He was forced to leave the rest of the page empty, drew a picture of a cat and cursed the creature with the following words:
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."
Paws, Pee and Mice
You can also check this article:
Cats on keyboards? It's a long ancient tradition.