Character mistake: After firing Percy and Baldrick, Edmund says to Baldrick that he'll probably go back to shovelling dung in the gutter where Edmund found him. In the pilot episode The Foretelling, Edmund actually met Baldrick when Baldrick was pouring a drink for Edmund.
Other mistake: In the barn, the unknown, wounded knight offers ten thousand sovereigns. At that moment, on the floor, he lifts his arms. A small sticker is visible on the inside of his left shoulder plate. (No doubt a label that wasn't expected to ever become visible.)
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. (00:15:45)
Revealing mistake: It is apparent that the door Flash pushes Percy through is fake. The door bends inwards like polystyrene when it should be made out of wood.
Revealing mistake: The bomb that is thrown at the Prince explodes before the lit fuse actually burns down far enough. (00:03:15)
Factual error: When Blackadder has disguised himself as the Prince and is speaking to Wellington, Wellington says, "I have with me here the most recent briefs from my General in the field". Blackadder, deliberately misunderstanding, replies "If you would like to pop them in the laundry basket". Blackadder is referring to the short, tight style of men's modern underwear, known as briefs, which were not invented until the 1930s.
