Casey is depicted as having been taught to handle firearms from toddlerhood, yet when she uses a shotgun she racks it and fires with an empty chamber — even though she's shown checking and then loading her final two shells.
When Dr Fletcher receives Kevin's first e-mail, the subject field displays 'We need you;'. However, when she opens the message, the subject line reads 'No subject'.
By the end of the film, Casey's make-up and hair remain immaculate despite having been held hostage, scurrying about the grimy maintenance basement and battling the Beast.
Directly before Dennis knocks Claire and Marcia unconscious in Mr Benoit's car, he locks every door, yet moments later Casey opens the passenger-side door, which is plainly shown to be unlocked.
Towards the end, as Dr Fletcher writes the note, you can track the movement of her hand and clearly see the word "name" penned in all lower-case letters. However, when the camera later reveals the note, the same word is shown in entirely capital letters.
When Casey is knocked to the ground and tries to fire at The Beast, her left hand shifts its grip on the shotgun as the camera angle switches.
When viewers are introduced to the psychiatrist character, a news bulletin about the missing girls is shown. Two of the three photographs displayed are not of the actresses who portray those girls in the film; only Anya's actual picture was used.
On their initial attempt to escape, as Claire runs down the corridor, a shadow from the camera or other production equipment is visible across her.
As the camera moves in on the father placing food into the boot, you can see the camera crew's legs reflected on the car's wing.
The character Dr. Fletcher is portrayed as a psychiatrist, which indicates she would hold a medical degree rather than merely a Master's in counselling. A person with only a Master's degree would not be addressed as Dr.
When Casey boots up Kevin's computer in the locked room, it displays 10:25 am even though it is actually night-time in the film. However, the computer is shown to be disconnected from the internet, so the clock could simply be incorrect.
When Claire hides inside the locker, the ventilation slats are visibly above her head, yet the shot filmed from within the locker places the slats at Claire's eye level.
There is no reason why the other alters could not simply notify Dr Fletcher of the problem directly by sending emails about it, rather than merely arranging appointments.
While Casey describes how she realised The Beast's strength, she claims she saw him lift one of the girls onto the bed as if she were weightless. Yet Casey is the last to come round from the sedatives — the other two had already woken.
Casey would not have been placed in a police vehicle after sustaining such a serious leg wound; after the initial dressing of the injury in the ambulance, she would have been taken straight to hospital for treatment and a thorough examination owing to the nature of the offence and the severity of her injury.
In the close-up shot of Dr. Fletcher's degree scroll from Tulane University, the phrase "school of political sciences" is misspelt as "political scineces". In addition, a Master's degree in Psychology would not ordinarily be awarded by a school of political sciences.
When the Beast emerges from behind and seizes Dr Fletcher, her spectacles are visible just above his arms. In the ensuing shots, as the Beast steadily tightens its grip, the spectacles have vanished.
