When chanting the Litany of the Saints, the order in which the Saints are invoked is not in the correct order.
When Cadfael handles the skull of the dead man, it is obvious from its weight in his hand and the sound that it makes when tapped, that it is made of plastic.
When Cadfael is examining the body from the sack, the dead body is clearly breathing.
Natasha Little, playing Melangell, is quite clearly wearing modern lipstick. This is most obvious when she and Cadfael are discussing whether her brother can really walk.