Visible crew/equipment: When Blackadder is called to the Queen's first practical joke and he says he didn't laugh because his head would fall off, the Queen says, "If you don't start soon, your head will fall off", the boom mike is visible above her head. (00:09:55)
Revealing mistake: When Percy is holding the 'Green' in his hands, light of the green reflects on the wall behind Blackadder. However the way Percy is holding the 'green' in front of Blackadder, Blackadder's shadow should be on the wall behind him, but it isn't. It's obvious green lighting is used to light up the back wall. (00:18:20)
Visible crew/equipment: When Edmund returns to his house and complains about the smell as he enters, the edge of the set is visible on the extreme right of the picture, just before the camera zooms in on him.
Answer: According to the IMDB.com's quote page for Blackadder The Third, it's "Aahhhhh. Hot potato, orchestra stalls, Puck will make amends. Owwwwww."
Gary O'Reilly