Plot hole: If the Lady of the Lake walks every night to her room and kills those in her path, why didn't Flora and Miles' parents die in their room by the hands of the Lady in the Lake when they first moved in?
Continuity mistake: Kurt is still recovering from the beating he took in the previous episode with bad cuts on his forehead, checks and temple area. They are red and impossible to miss while he is in the police station. The cuts have miraculously disappeared in the next scene when he goes to visit Mona.
Revealing mistake: The bullets the priest takes out of the ammunition tray have no primers. (01:01:33)
Factual error: A British soldier in 1940 says he was educated at the University of Warwick. The university wasn't founded until 1965.
Continuity mistake: When Eden confronts Kinsey by the lockers, as the angle changes so does Kinsey's arm. In some shots, she has her arms crossed and the locker door is closed, in some shots she has one arm up, holding the (open) locker door.
Factual error: In Massachusetts, Atticus, Leti and George are attacked by the local sheriff and his deputies, who are patrolling the county roads. In Massachusetts, sheriffs run the county jails, but they do not (and did not) handle routine policing, which is the responsibility only of municipal police departments.
Continuity mistake: The three friends finally meet in person after all the texting. Karube brings a cigarette to his mouth when Chota asks "Where to?", but in the next shot his hand is lower. (00:07:15)
Angel of Mercy: Part Two - S1-E4
Character mistake: When Lenore Osgood is speaking on the phone with Charles Wainwright about killing Dr. Hanover, she mispronounces "Larynx" as "Lar-nix."
Continuity mistake: Throughout the series, the Barbers pull their cars straight up their driveway. But the cars are nearly always shown coming back down the driveway driving forward.
Revealing mistake: There are bullets placed on the counter, the one casing has a hole in it from being drilled to show it's a dummy round and there's no gunpowder in it. (00:14:45 - 00:15:20)