Visible crew/equipment: When Kate/Bob first arrives at Blackadder's and she says, "I'm an honest hard working lad", you can see the boom mike pop into picture above her. (00:04:55)
Visible crew/equipment: When Melchet is trying to entertain the Queen and she says, "No use, Melchet, I'm still bored," you can see the boom mike pop in above her head. (00:07:20)
Visible crew/equipment: When Blackadder is at the Queen's asking for permission to get married and she approves, the boom mike pops into picture several times above her. (00:20:10)
Visible crew/equipment: When Blackadder goes to see The Wise Woman, as she gets out of bed and starts talking you can see the boom mic moving above Blackadder's head. (00:15:50)
Visible crew/equipment: When Blackadder is at the doctor and the doctor says, "I think you are in luck though," while pointing at the board of "Principal Leech Points", you can see the boom mike pop in right above Blackadder. (00:12:45)
Revealing mistake: When Flash says "I've got a plan and it's as hot as my pants", his moustache is seen falling off.
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.
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