Cooked dragon flesh as a remedy for old age. Read al about it in the ultimate medieval guide to prevent and cure old age by Roger Bacon (c.1214-c.1294).
Cats leaving paw-prints and pee-stains in medieval manuscripts. An old blog post and its aftermath.
This blog post calls attention to a late medieval text which provides some practical advice to preserve books so that they may 'last forever' -some of these rules remain topical today!