In this episode, Percy shaves his beard off, yet it has returned in the next episode. This is because they were shown in the wrong order.
Flashheart's moustache starts peeling off his lip halfway through his scene.
When Flashheart pushes Percy through the throne room doors, they bend and break in a way that proper, solid wooden doors wouldn't and the entire wall wobbles.
In front of the Queen, Percy sings Pat A Cake, which did not come about until 1698, and Ring a Ring a Rosie not until the nineteenth century.
At the beginning, Edmund refers to the Hundred Years' War, which had certainly ended well over one hundred years before his time, but it was not called that until the start of the nineteenth century.
Half way through the scene with the doctor, a microphone can be seen dropping in the top of the screen for a second.
The wise woman that Blackadder visits suggests that he kill Bob. But Blackadder never mentioned the name of his servant to the wise woman so she would have no way of knowing Bob's name.