The Prodigal Son (1 & 2) - S2-E1
Revealing mistake: After Crockett and Tubbs' confrontation with the New York police at the end of part 1, as the police car drives away, in the background a blue car drives by and a man and woman can be seen in the car looking and pointing at the filming.
Revealing mistake: "Alan a Dale": Lady Mildred rides side-saddle. But when Gisburne gallops away with her, some shots reveal that the stunt woman riding the fast-moving horse is astride it full straddle. Her skirt is blown back just enough to see a brief glimpse of the stunt rider's real leg on the horse's right, and the fake pair of legs in side-saddle position on its left. For just a moment, the lady appears to have three legs. (00:20:00)
Revealing mistake: When the first scene at Emma's hideaway was shown, obviously the two characters Emma and Jessica were filmed seperately on the couch and then the film was put together (as both are played by Angela Lansbury). However Jessica did a lot of moving while she was talking, so Emma was looking straight across at where she had been, despite her bending down while she talked.
Revealing mistake: When the thief places The Blue Carbuncle in the goose's throat, it's obvious he actually doesn't put the gem in the bird's mouth. He pretends to, but then drops the gem into his other hand. This is all visible in the shot.
Another Song for Christmas - S1-E13
Revealing mistake: The smoke from the supposedly broken vehicle is obviously not coming from the tailpipe. It is coming from the trunk.