Revealing mistakes: When Mallory & Regan are thrown from the boat with their hands tied behind them, you can clearly see Regan put her hand out to steady herself as she "jumps in".
Revealing mistakes: In underwater scenes, marks are clearly visible on Mallory's face from a scuba mask. In no scene does Mallory have a scuba mask, so this is obviously from a mask she was wearing between takes.
Continuity: When Stanley has Mallory chained by the ankle to the floor in the soundproof room, he tells he has to wash her clothes and asks her to take them off and put them in a plastic bag. She is wearing blue jeans. In the next scene, the jeans are in the bag. How did she get them off? They would still be connected to the chain.