He applied the "Page 99 Test" to his new book, The Natural and the Supernatural in the Middle Ages, and reported the following:
Page 99 concerns the medieval discussion of dog-headed people. Did they exist, and, if so, what kind of creature were they?Read an excerpt from The Natural and the Supernatural in the Middle Ages, and learn more about the book at the Cambridge University Press website.
One author of the ninth century believed that the dog-heads lived in villages, practiced agriculture and had a moral sense (e.g. covering their genitals). So, even if they looked unusual, they were human.
In dealing with an alien belief, and attempting to show how medieval thinkers thought rationally even if their beliefs were different from our own, page 99 is a perfect example of the argument and the approach taken in the book.
Inside the Medieval Mind, BBC4, April 17 2008, is a television programme which is based on parts of the book, including the dog-head debate.