Revealing mistake: When members of Fight Club are starting fights, watch VERY closely when the guy with the hose sprays the vicar - you can see the camera wobble slightly (looking on the left of the screen at the top of the fence is a good reference point). This happened because the cameraman started to laugh. (01:15:10)
Revealing mistake: Just after the car crash scene when they are all crawling out of the car, a large drop of rain is seen in the very top left of the picture. The drop is too large and falls too slowly to be an actual drop of rain. This shows there is an umbrella type thing protecting the camera from the water. (01:41:10)
Revealing mistake: When Brad Pitt is cutting out newspaper articles about Project Mayhem's mayhem, the headlines refer to their deeds, but the actual writing in the articles has absolutely nothing to do with the movie. They seem to all come from one article about some town council meeting. (01:21:10)
Revealing mistake: Before the final fight scene between Tyler and the narrator, Edward Norton points a gun at Tyler telling him to step away from the van. Tyler breaks the key and throws it away. When this shot is seen through the security footage, then in the far left security computer screen we can see that there is already a gun shot hole in the back window of the van, and there is also some random guy walking in the top left corner of the screen. (02:07:35)
Continuity mistake: Close to the end when Edward Norton runs up to the front of the empty building and Brad Pitt appears, he tries to break the glass door by pushing a bench into the door, but it doesn't work. He doesn't move the bench and he then shoots at the glass and breaks it. When it shows him walking through the broken door, the bench has disappeared. (02:05:10)
Trivia: There are several places where Edward Norton sees Brad Pitt for a split second before he actually meets him - beside the photocopy machine, talking to the doctor, at the testicular cancer group, when Marla is in the alley, and when watching TV when the waiters say "Welcome". Also Tyler is the one who steals the Camaro after Tyler and the narrator meet for the first time.