Continuity mistake: A few minutes after Lee puts a bandage on Hugh's forehead, it disappears completely in one shot (as does the cut it was covering), before reappearing a moment later, but in a different position.
Visible crew/equipment: After Emily attacks the "other Emily" in the bathroom, she leaves, and walks through a doorway to rejoin the rest of the group (just before she collapses). If you look at the alcove type doorway adjacent to the group you can see the head of the boom microphone slowly move into the shot then slowly move out again. (01:20:04)
Visible crew/equipment: Near the beginning when everyone is sat at the dining table, Hugh asks if anybody other than him is having trouble getting reception on their mobile phones. Then there is a reaction shot of Emily and then another cut to Lee laughing and holding her glass of wine. In this shot of Lee you can see the living room behind her and if you pay attention you can see a crew member (possibly holding a camera) who appears to be crouched behind the sofa, raise his head into the shot. (00:07:15)
Visible crew/equipment: When Kevin and Emily are alone in the dining room and Kevin asks her if she wants to go on a trip with him to Vietnam and Emily says she needs more time to think about it, you can see a cameraman sat on the other side of the table filming them. The filmmakers have tried to obscure him by placing a wooden table chair in the foreground but you can still see his arms/elbows between the chairs slats. (00:05:54)
Visible crew/equipment: At the beginning, when Mike, Beth and Lee are in the kitchen, immediately after Mike asks Beth "How long have you been cleansing for?", Beth answers and you can see a camera lens in the bottom right corner of the screen filming the actors. (00:02:11)
Audio problem: When Mike returns from blackmailing the other house he is confronted by Kevin who asks him where he has been. At one point during Mike's explanation he says "I was gonna smash the window and take the book", however his mouth movements do not match this. (00:45:08)
