Continuity mistake: When Al and the two masked people are attacking Tris, Four appears, throws Al off Tris and he hits the wall. As Al hits the wall, it appears to have nothing lit on it, then from a side angle, green lighting has suddenly appeared. This has nothing to do with the camera angle. (01:19:40)
Continuity mistake: When Tris and Four kiss, Tris is shown putting her hand around the back of Four's neck. Next shot, her hand is suddenly on the right side of his neck. (01:31:25)
Continuity mistake: Mind-controlled Four grabs Tris by the neck and pushes her against a stone column. First, Tris is pushed against the edge of the column, then she's being pushed against the middle of the column, then the edge and a few shots later, back to the middle of the column. (01:58:30)
Continuity mistake: At the choosing ceremony, people cut themselves on the hand and put it in the bowl of each section they want to join. However, when Tris chooses Dauntless, the bowls look clean and the knife is clean. There hasn't been enough time to wash them.
Continuity mistake: In the last train scene with Tris and Four the tattoo seems gone from Four's neck. In some scenes, his tattoo was higher up on the neck.
Revealing mistake: Natalie Prior appears to be breathing when she's dead.
Answer: It's typical for movies to delete or dilute various plot elements from a book source. The movie's running time is a factor, and eliminating characters, side stories, combining plot points, etc. streamlines the plot. The movie chose to keep the focus on Tris and Four.
raywest ★