Continuity: Although Casey is shown following and reiterating Sofi's instructions to destroy all of the mirrors in the house and then burn all remaining pieces of them, when Romy enters the home a few scenes later, the mirror over the mantle is shown with sizeable pieces remaining.
Revealing mistakes: The contact lenses used to give the "heterochromia" effect are incredibly obvious. The blue sections cast shadows on the brown iris below.
Anachronisms: The photo that shows the main characters uncle is a Polaroid, however Polaroids weren't invented until 1948. Her grandmother, Sofi says he died in 1944 in Auschwitz.
Continuity: At the ending scene, when Casey runs on the bridge, the surface of the road seems to be dry, but in the next scene, it is wet.
Continuity: (At 35:00) Casey is using her laptop on her bed, she closes it and leaves it sit, then she turns off the lamp and climbs into bed and the laptop is gone, you see a light spot in the bed that could have possibly been it, but later when she awakes from a nightmare the computer is definitely not there.
Revealing mistakes: When Casey is surprised by the "visitor" in her medicine cabinet and is on the floor, she leans against the door and the toilet behind her shifts indicating that it is a prop toilet, not bolted down as it should be.
Continuity: When Romy hits the boy with her car, she closes the door when she runs to check if he's okay. When she runs to get in her car, the door is open.
Revealing mistakes: In the link between the movie reel and nightclub scenes a train is shown going past in reverse. The audio is convincing, however the headlights on the train give it away. The cars under the bridge are also in reverse.
Continuity: In the club scene, after entering Mark asks Casey, Romy and one other girl if he can get any a drink from the bar. Romy and the other girl orders a drink. Casey says no. As soon as Mark walks away to complete the order, Casey begins to walk through the club already holding a drink.
Incorrectly regarded as goofs: What appears to be a mistake is not. When Odette Yustman's character meets with the Rabbi, he opens the book from left to right. Hebrew texts are written the opposite way of English, so the book should have been opened from right to left; but the rabbi had no way of knowing that the book was written in Hebrew and the cover and latch are of a book bound in the left to right style. He proceeds to read from right to left for a few seconds and then appears to jump around a bit. It is possible that the book was bound by someone that was not Jewish or familiar with Kabbalah, or wanted to conceal its writings. It is also possible that it was a series of small writings therefore his reading and turning of the pages would make sense even if the book was inside a traditional left to right binding.
Revealing mistakes: When Romy chats with Casey via webcam, the light on the webcam on her MacBook is off, but it should to be on.