A black hair grip appears in the Dolma's hair out of nowhere and then moves around between shots during the cauldron lake scene.
When Arthur is standing in the water of the cauldron (and not yet walked into the water up to his chest) and encouraging Guinevere to walk into the water of the cauldron, water is dripping off his arm and glove from the previous take.
Several shots of Arthur carrying 'Gwen' reveal her to be a rigid life-like doll. Notably in the rocky gorge when Merlin tells him to carry her to safety away from the dragon.
When the Dochraid is calling out a spell, the actress's real teeth can be seen behind the false ugly ones.
The Dochraid's voice narrates her raven-flown message as Morgana reads it. The spoken words do not match what is written on the parchment.