Gerald of Wales quotes
Although he was completely illiterate, if he looked at a book which was incorrect, which contained some false statement, or which aimed at deceiving the reader, he immediately put his finger on the offending passage. If you asked him how he knew this, he said that a devil first pointed out the place with its finger...When he was harried beyond endurance by these unclean spirits, Saint John's Gospel was placed on his lap, and then they all vanished immediately, flying away like so many birds. If the Gospel were afterwards removed and the History of the Kings of Britain by Geoffrey of Monmouth put there in its place, just to see what would happen, the demons would alight all over his body, and on the book, too, staying there longer than usual and being even more demanding.
Gerald of Wales