Continuity mistake: When McAngus empties his bag on the table and the head falls on it we see the back of the head is turned against the camera. When it cuts to a close up of the head the head is facing in the direction of the previous camera take. When it cuts again the back of the head is turned against the camera.
Continuity mistake: After Blackadder talks to Baldrick and Percy about the plan, Blackadder walks to the window to notice MacAngus getting on a horse to exit the castle. The shot where Blackadder walks over to the window shows only one window above the window Blackadder looks out of and nothing more. A couple of shots later when the camera is in front of Blackadder, two extra windows have appeared from nowhere. There was an iron maiden there which could have blocked the view, but at least six inches of wall are shown between the iron maiden and window, so the window couldn't have been blocked by it. Not to mention the window panes are in a grid of 3x3 from inside, but 4x4 from outside.