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.
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.
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.
Toward the end when Dr. Fletcher writes the note, you can make out her writing the word "name" in all lowercase letters by following her hand motion. Later when the camera actually shows the note, it's written in all capitals.
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.
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 Master's Degree is not referred to as Dr.
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.
When young Casey Cooke was in a make-shift hunting blind learning to hunt, it was obviously in the fall time because the ground was fully covered with colored leaves that had fallen from the trees. In the same scene, you can clearly see that all of the trees had thick green leaves on them indicating that it was not that late in the fall season.
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.
When Casey starts up Kevin's computer in the locked room it reads 10:25am when it's actually night time within the movie. However, the computer is then shown to be disconnected from the internet, therefore it is possible for the clock to simply be wrong.
When Claire hides in the locker, the ventilation slats are clearly higher than her head, but the scene shot from within the locker places the ventilation slats at Claire's eye level.
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.
When the camera approaches the father putting food in the trunk, you can see the camera crew's legs in the reflection in the fender of the car.
The track of camera dolly clearly seen on the ground behind Claire before she hides into the locker.
There is no reason why the other alters couldn't just directly alert Dr. Fletcher of the problem by sending emails about that instead of merely arranging appointments.
When Casey is explaining how she knew The Beast was strong, she says she saw him carry one of the girls to the bed like they weighed nothing. But Casey is the last to wake up from the drugs- the other two girls were already awake.
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.