Continuity mistake: When the narrator first meets Bob, Bob starts telling him how he used steroids. In one shot we see the narrator's right hand is resting at the middle of Bob's back, but in the next shot we see his right hand at the top of Bob's back and a little above his armpit. (00:08:10)
Continuity mistake: In the scene in the bar right after Edward Norton's apartment blows up, watch the men playing pool behind him. Towards the end of his conversation with Pitt, there is a continuity error. One of the men is bent over getting ready to take a shot. A mere second later, he's on the other side of the table and his opponent is finishing his own shot. (00:29:40)
Continuity mistake: When Jack asks Tyler if he can stay at his place, there is a glass bottle on the payphone to the left. When the shot changes from the far shot to the close shot, the bottle is further to the right. It's back to the left when the far shot comes up again. (00:30:40)
Continuity mistake: When Marla's wearing the wedding dress, she grabs Rupert by the crotch. The second shot, a cigarette suddenly appears In her hand out of nowhere. (00:47:00 - 00:48:00)
Continuity mistake: When Tyler Durden goes to Marla's apartment to prevent her suicide, he removes a cigarette from his mouth and gestures as if he is throwing it down on the floor at the top of the stairs. Then the cigarette is back in his mouth when he proceeds to the door, at which point he really does throw it down on the floor. (00:50:30)
Continuity mistake: When Tyler gets beaten up by Lou, his mouth is bleeding after the first punch. After maybe two punches Tyler jokingly claims to "get it", then he says he "lost it". Right then the blood is no longer there. (01:12:25)
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)
Continuity mistake: When Ed Norton is blackmailing his boss the thermostat changes from white to black in some of the shots. The chair moves a bit to the left too. (01:16:00)
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)
Continuity mistake: When they are preparing to confront the City Councilman, Brad Pitt's character pulls him in to the bathroom. If you really look at the locks on the door you see that as he is pulling him in there is no deadbolt lock, but when the Councilman is halfway in through the mirror you can see that the same door has a deadbolt lock. (01:33:45)
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: In the scene where Ed Norton discovers that Meat Loaf's character has been killed, you can clearly see him breathing in the long shot while he is lying dead on the table. (01:46:15)
Visible crew/equipment: During the police interrogation The Narrator is pinned to the table, after he gets the gun and rolls back off the table you can easily see the power pack attached to his back/underpants during the roll. (01:58:10)
Continuity mistake: Check out the sweat stain around the collar of Ed Norton's t-shirt in the scene towards the end of the film where he is being interrogated by police. It keeps getting bigger and smaller from shot to shot. (02:00:50)
Revealing mistake: Towards the end of the film, when the narrator and Tyler are fighting in the basement, Tyler slams the narrator's head into the wall by the van. For a split second, before the shot changes, the 'concrete' wall visibly buckles inwards. (02:03:35)
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)
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: Near the end of the movie in the underground car park, Brad Pitt pushes Edward Norton into the wingmirror of a van. The mirror flips back against the van and stays there. A couple of shots later we see Brad Pitt check his face in the mirror, which is at a different angle to what it was before. (02:08:45)
Continuity mistake: Near the end of the film when Tyler throws Ed Norton down the steps we get the view from a security camera, however we can see the camera we are supposed to be looking through in the top right hand corner. (02:09:10)
Revealing mistake: When Brad Pitt throws Edward Norton down the stairs, there's a shot close to the bottom of the stairs in which you can see the stunt-man's face. (02:09:15)
Answer: After he realized Tyler's true nature at the hotel, Tyler made many phone calls. Jack called the same phone numbers and realized that they corresponded to the buildings mentioned on the Project Mayhem folders. He had to confirm this, so he called a couple different buildings. He tried to tell the building operators that something was up, but they're already assisting Project Mayhem and could not be dissuaded. In desperation Jack went to the police...
Phoenix