When the girl is kidnapped in the parking garage and after she and Stargher have hit the ground, the dog is heard barking at the struggle. However, we can clearly see the dog in the shot and he is simply lying there calmly, not barking.
Though "Whalen's Infraction," a brain disorder which is said to have accelerated Stargher's schizophrenia was made up for the movie, an infraction actually refers to an incomplete bone fraction and affects bony tissues, not the brain. Cerebral infarction ("infarct" instead of "infract"), or tissue death due to lack of blood flow, does occur in the brain, but this is said to cause schizophrenia-like symptoms and would not cause or affect schizophrenia itself.
Just before water pours on Julie, the monitors around the room show her eating (at least, holding food). But when the camera cuts straight to her, she isn't holding anything (error caused by deleted material).
During the second filling of the cell the cameraman, and possibly the director (another person is seen next to the cameraman), can be seen in a reflection on the inside of the cell. When the camera pans to the left as Julia pounds on the glass walls and curses out her captor, you can see two figures (one with a camera) reflected in the glass.
Any goofs occurring in the "subconscious" world which the characters enter, do not have to be consistent or conform to realistic physics, as the subconscious is arbitrary, and can create whatever rules it wants.
The gemstone on Julia Hickson's engagement ring is tucked under her hand when she is looking for loose fits, thus making it appear to be a wedding band (though she isn't married yet). The stone is visible when she yanks on the pipe.