That's the book I finished over the weekend, edited by Edward Peters.
There were all sorts of interesting tidbits, but this is my favorite heretical peasant belief, for many reasons, all obvious:
"The souls of the dead do not eat, but they do drink good wine and warm themselves at fires. The wine is not, however, diminished by their drinking it." (p. 258; from "The Inquisitorial Register of Jacques Fournier," compiled between 1318-1325).
Then there was this accusation against the Cathars, written about 970: "Do you see, brothers, how thoroughly damned they are, rejecting holy baptism and feeling an aversion to baptized children? If it happens to them by chance to see a child they shrink from it as from a bad smell." (p. 114) Ha ha ha!
As I finished the book, it occured to me that, according to the medieval authorities, I'd guess that every Christian existing on the planet, including the Catholics, would be considered heretics. And therefore totally burnable. That's progress!