Crew or equipment visible

When the girls attempt to escape the first time and Claire runs down the corridor, you can see the camera/production equipment casting a shadow on her.

Revealing mistakes

Casey would not have been put in a police car after suffering such a severe leg wound, but after the initial dressing of the wound in the ambulance, she would have been transported directly to the hospital for treatment and a full examination because of the nature of the crime and the severity of her injury.

Continuity

When Dr. Fletcher receives the first email from Kevin, the subject reads "We need you;" however, when she opens the email, it says "No subject" in the subject line.

Continuity

At the end of the movie, Casey's makeup and hair are perfect despite being held hostage, running around in the filthy maintenance basement and fighting with the beast.

Continuity

When Hedwig finishes his dance for Casey, he switches off his CD player which causes it to open. In the next shot it is closed.

Continuity

The Beast is shown taking a bite out of Casey's calf, badly enough to cause her to limp for the rest of the movie; but, at the end, as her leg is being wrapped in the ambulance, the EMT grabs and squeezes her calf right where the injury would be. Casey doesn't flinch or react at all.

Crew or equipment visible

When the camera approaches the father putting food in the trunk, you can see the camera crews legs in the reflection in the fender of the car.

Factual errors

There will be no alarm if you open a passenger door of a car with the keys in the keyhole. Alarm will sound only for the driver's door.

Revealing mistakes

In the close-up shot of Dr. Fletcher's degree scroll from Tulane University, the school of political sciences is misspelled as "political scineces". In addition, her degree of Master of Psychology would not be awarded by a school of political sciences.

Continuity

When "Dennis" brings the girls' sandwiches, you see Marcia pick up half of the sandwich and take a bite, but as he leads the girls to the kitchen, the sandwiches on both plates are shown uncut (whole) and there are no bites.

Factual errors

When she is loading the shotgun, it breaks over and loads from the breech. This makes it a single shot, but later on she is holding the gun and cocks it by pumping it. A breech loader only has capacity of one shell per barrel.

Continuity

Kevin is counted as one of the 23 personalities inhabiting Crumb's body as shown by the video logs on his computer. Dr. Fletcher is emailed 20 times by him to warn her about the Beast, which suggests 20 of the 23 personalities emailed her. As Dennis, Patricia and Hedwig are the personalities who want to welcome the Beast, it is believed none of them emailed Dr. Fletcher, which accounts for the three missing personalities. And since Kevin is one of the 23 personalities, it would suggest he is one of the personalities who emailed her. However, when Casey states Kevin's full name to bring him "into the light", he reveals he has no memory of any event since September 2014, which shows that he hasn't "taken the light" for two years, so he could not have emailed Dr. Fletcher.

Continuity

When Dr. Fletcher interviews Barry about the incident that happened at his work, we see her without glasses. In the next shot (from behind Dr. Fletcher) we see her remove her glasses.

Character error

The Dr. Fletcher character is said to be a psychiatrist, which would mean she has a medical degree, not just a master's in counseling. A person with a masters degree is not referred to as Dr.

Factual errors

When Dr. Fletcher is giving her speech through Skype, you can see her being projected onto the large screen for the audience. The video on that screen is completely synchronized with the small image on the bottom right, but it should be delayed, as the video signal has to first travel there, be projected on the large screen, recorded by the second camera and finally sent back to her computer. Note: If the internet speed is not an issue, it doesn't matter how many feeds its going through, it still travels at the speed of light and one would not notice any delay. Live TV shows have added a delay only due to the Janet Jackson incident at the Super Bowl.

Continuity

When Casey is running from the Beast, she is attacked in the gate between sections, causing her white shirt to be torn on her front and right (audience left) shoulder. When she is in the cage at the end of the corridor, she has to reload after firing and missing yet another shot. In the medium close-up on her left arm holding the shells, the sleeve is badly torn and dangles at her wrist. In the next shot, Casey gets frustrated with the same sleeve and pulls it off her shoulder to where it was at in the previous shot.

Revealing mistakes

When the Beast comes up from behind and grabs Dr. Fletcher, her glasses are present just above his arms. The subsequent shots when the Beast continually increases pressure, her glasses are no longer there.

Character error

Casey is shown having been trained since she was a toddler to use firearms, yet when she does use a shotgun, she racks and fires on an empty chamber, even though she's shown looking at and then loading her last two shells.

Character error

When Dennis is in the train station after Patricia has bought flowers to lay on the train platform, an extra who is walking behind Kevin can be seen looking directly at the camera.

Continuity

When Casey is knocked down and attempts to shoot The Beast, her left hand changes position on the shotgun as the camera angle changes.

Factual errors

Immediately before Dennis knocks out Claire and Marcia in Mr. Benoit's car he locks all the car doors, but a moment later, Casey opens the passenger side door, which is clearly shown to be unlocked.