Father Andrew Kiernan states that monks invented alcohol. Even if one grants Kiernan the benefit of the doubt and assumes that he is referring exclusively to alcoholic beverages, he is still wrong. The ancient Egyptians were drinking beer back in 3000 B.C.E., if not before.
The same 1977-81 Pontiac Firebird is seen three times. It
shows up two times in the same scene. Frankie is almost hit by the car in the baby scene. She climbs over the hood in the crown of thorns scene and a moment later it drives past as she runs down the street.
Right before Frankie receives her first wounds as she lies in the bathtub, a bird flies in the room. When the bird flies off a single feather drops into the tub. As Frankie picks up the feather with her right hand, the bloodless wounds are already visible on her inner and outer wrist.
When Frankie is being wheeled down the ER hallway near the beginning of the film, she is wearing pink lipstick (strange enough, since she just came from the bath). But moments later when she is revived on the ER table and the doctor is talking to her, she is wearing dark red lipstick.
When shown an overview of the building at night Frankie (or her double) is clearly seen (against the night sky) sitting on the edge of the building (this comes before the actual scene in the movie). The mistake is pointed out by the director in his DVD version commentary
The subway interior shots correctly show a Pittsburgh subway car, but some exterior long shots show a car clearly marked with the logo of the New York Metropolitan Transit Authority. The exteriors were reused from Money Train (see trivia).
After Frankie opens the package from her mother which contains the rosary, she is seen walking over to the table. She is holding a cup in one hand and picks up the rosary in the other. The next shot has the items in her hands reversed.
When Frankie is in the bath she is eating an apple at the beginning of the scene which she puts on the bath ledge. However, when Frankie is putting the wet feather down and when she is being pulled back into the water then the apple is no longer there.
When Frankie Paige receives a package from her mother containing, among other stuff, Father Almeida's rosary, the Post Office stamp on it reads "BRAZIL", when the correct spelling in Portuguese-speaking countries is "BRASIL".
In the scenes in Brazil, people are speaking Spanish and Portuguese with Portuguese accents, not Brazilian accent. It would be like an American countryside movie with English actors playing the roles with cockney accent.
The plot centers on the supposed ban of "Gospel of Thomas". In fact, this gospel (along with many other gnostic or non-canonical texts) was never officially suppressed by Catholic Church and its translations can be freely bought in bookstores.
In the bathtub scene, we see numerous shots of Frankie suggesting she is completely naked in the tub (without seeing actual nudity). Right after she places the fallen feather on the side of the tub, the unseen "force" pulls her backwards into the water. As she is falling back, we can clearly see she is wearing a flesh colored bra or bikini top.