Double Sin - S2-E6
Continuity mistake: Madame Durrant is showing the niece the medallions she is supposed to sell. In close-up you can see her holding the suspension ring with her right hand, and her left hand too, on the side, with the thumb on it. But in the wider shot, she is using merely the side and back of the left hand for support, the thumb being at distance from the jewel. (00:08:20)
Double Sin - S2-E6
Continuity mistake: Poirot has just been 'beastly' with Japp, in Hastings' words. In the establishing shot of the town square before the bus, a woman in orange (Miss Durant as we'll learn) pass by the ice cream cart. That same woman passes again the same spot as the camera is behind the cart, following the policeman and then getting Poirot and Hastings in frame. The driver and the man he was talking to are also in a different spot as that happens. (00:11:10)
Double Sin - S2-E6
Continuity mistake: In the car chase, when the woman turns to check the police behind them, the close-up on the steering wheel does not match the position of her hands before and after. Similarly her passenger has the right hand visible when it shouldn't be. (00:28:45)
Double Sin - S2-E6
Continuity mistake: When Hastings storms out of the antique store claiming to have solved the case, Poirot follows him until he turns into an alley. In the view from the back of the alley, there's a man with a hat who walks all the way past Poirot and turns the corner into the main road. In the reverse angle, the guy is still walking down the alley in front of Poirot. (00:42:30)
Double Sin - S2-E6
Continuity mistake: At the end of the episode, Hastings flips the cutting, having the left palm on the back of it. Next shot, and he's holding it by a corner. (00:50:45)