Continuity mistake: When Blackadder, Queenie and Nursey are all comforting Melchett, there is a shot from the side view of Melchett, he is holding his head with his left hand. Then there is a shot from behind Melchett, he still has his hand on his head but when the shot returns to the side, Melchett no longer has his hand on his head.
Continuity mistake: When Blackadder and the other soldiers are about to go "over the top", you can see two other soldiers standing behind Darling. They are presumably in the upper part of the trench. When Blackadder blows his whistle, you see all the soldiers climb onto their ladders and then start to rush over, side-by-side. In the next shot, when we see the soldiers emerging from the trench in slow motion, the other two soldiers are still back in the trench waiting for Darling to climb out before they move, as the two shots were filmed in two different studios.
Continuity mistake: When Blackadder, Baldrick and George are out in the no man's land, Blackadder screams and Baldrick asks why. Blackadder answers he put his elbow in a blob of ice cream while looking at Baldrick. When it cuts he is looking straight forward instead. (00:22:20)
Factual error: In Blackadder's Christmas Carol, during the Elizabethan part of the 1988 Christmas special, Queen Elizabeth asks Edmund if he has any last words before she chops off his head and sticks it on the Christmas tree. Christmas trees weren't introduced to England until Prince Albert (husband of Queen Victoria) brought it from his homeland in 1840.
Audio problem: "Blackadder Back and Fourth": Blackadder and his guests are going to the cellar where the time machine is kept. While they are going down the stairs, Blackadder says, "To his exact specifications." However, his mouth is shut and his lips don't move. (00:03:35)