Regarding the opening panel, while it may be true that swords were smeared with excrement (I don't know if that's the case or not), the intent to cause infection cannot possibly have anything to do with it. In those days there was no conception of what infection was, or that cleanliness or not had anything to do with it. Illnesses were ascribed to all sorts of mystic nonsense, including demons and the disfavor of God, and were often treated by bleeding.
It wouldn't be for a few more centuries until microorganisms would be discovered, and their role in infection and the effect of cleanliness on infection become understood. Even when these things were discovered, it took time for them to become accepted and prior beliefs to fall by the wayside.