Other mistake: When Theo is thinking back to when Steve offers to share the royalties from his book, Shirley is heavily pregnant with her daughter. However, on the table next to Theo, is a photo of Shirley's son and daughter, as they are in the present.
Other mistake: When Steven is giving his final monologue, Michiel Huisman's natural Dutch accent slips through when he says "Without it, we cannot continue for long to exist sanely under conditions of absolute reality."
Other mistake: While working in the basement, the young Hugh Crain gets his right hand sliced badly by a fan. When the story next jumps forward to the present time, the first thing we see is Hugh grabbing a handful of dirt with the same hand and there is barely a scar on it.
Visible crew/equipment: When Olivia is saying goodbye to the children, when she leans in to talk to Luke if you look at her left hip you can see a microphone pack sticking out. (00:22:02)
Continuity mistake: Just before Olivia commits suicide by falling from the staircase balcony, we see her behind the railing. How does she suddenly get in front of the railing (which would need to happen in order for her to fall) just as the ghost of Poppy reaches for her? (00:52:15 - 00:53:00)
Open Casket - S1-E2
Other mistake: When Theo says that she thought Luke was in rehab, Shirley says that he was "until this morning" and that he "flew the coop." In reality, Luke left rehab the previous day.
Visible crew/equipment: While Theo explores the basement of the Dunlaps, the family of one of her patients, a boom mic can be briefly be seen in the upper right corner. (00:19:31)
Revealing mistake: Just after falling to her death from the balcony, Olivia's corpse adjusts her arm toward her body. (00:53:30)