Continuity mistake: When Frank is fishing the pen out of the fish tank and the fish gets attached to his nose, there is visible blood. When the camera cuts back to Frank, the blood is gone. (00:20:35)
Continuity mistake: When Frank is at the party when the queen arrives, before the horns blow in his ears he's about 1 foot away from them, but the close up of him shows his ears even with the end of the horns. (00:56:50)
Continuity mistake: As Frank and Jane head back to her apartment, a woman passes them by with her dog. When the camera cuts to Frank several times in the scene, you'll notice that the woman and the dog are in several different places and end up turning the corner twice. (00:42:25)
Continuity mistake: When Nordberg is in the hospital for the first time, Frank comes. Before he walks in, Nordberg's hand is on his side, and when Frank finally walks in, his hand is on his stomach. (00:10:05)
Continuity mistake: When Drebbin is riding in the back seat of the "driver's ed." car, the gear shift stays in the same position even when the car is reversing. (00:32:45)
Continuity mistake: When cutting into the cake with the queen's portrait on it, the waiter slices across the inner corner of the queen's right eye. However, the two pieces of cake served to Jane and Frank both have complete and uncut eyes. (00:54:25 - 00:54:55)
Continuity mistake: When Frank has his speech and says "No matter how silly the idea of having a queen..." you see the mayor turning her head to the right. When it cuts she is looking to her left with a rather shocked face. (00:13:55)
Continuity mistake: In Ludwig's office, the position of the tissue papers changes between shots. (00:21:20)
Continuity mistake: When Nordberg stumbles out the door on the ship and about to fall over the rail you see him going out the cabin crouching with his head first. When it cuts to a wider shot from outside you see him walking calmly against the rail before falling over. (00:07:00)
Continuity mistake: When Jane is sucking on Frank's finger, you see Jane holding his finger. When it cuts, she isn't holding his finger. (00:36:40)
Continuity mistake: In the beginning of the movie when the guy with the long beard starts to talk you see Frank standing disguised by the table. When it cuts Frank is moving towards the table. (00:01:25)
Continuity mistake: When Frank sets Lugwig's place on fire and goes out the window, you see him about five or six windows away from the corner. Although in the next shot of him, he's going around the corner. (00:46:45)
Continuity mistake: When Frank is in his apartment and when Jane leaves Frank is facing toward the fridge but the next shot of him his back is facing the fridge. (00:51:40)
Continuity mistake: In the scene where Frank is in the driving school car chasing the doctor, right after Frank says, "I know a shortcut. Turn left here", we see two brief shots of the doctor's car, one from the inside of the car and the other from the outside as he is turning around a corner. In both shots the rear window is shattered. However, it is only four shots later that Frank shoots at the doctor's car, shattering the then intact rear window. (00:31:45)
Continuity mistake: In the beginning of the movie, during the big fight, Frank grabs Mikhail Gorbachev and smashes his head through the wall. The guy stays there but at the end of the fight, when Frank is about to jump out of the window, it shows him again. The hole now is bigger and not only consumes his head but all the way to his waist. (00:02:15)
Continuity mistake: When the "I LUV YOU" picture is viewed in Nordberg's hospital room, the photo has a vertical/portrait orientation. When Frank shows the picture to Jane, the photo has a horizontal/landscape orientation. (00:12:50 - 00:38:25)
Continuity mistake: When Frank does his speech at the end, his chest protecter goes from being wrinkled and squished in one shot, to perfect condition in another, and then back to wrinkled again in the next. (01:17:30)
Continuity mistake: When Ludwig picks up his gold box you see him holding the box in different ways between the shots. (00:20:10)
Continuity mistake: When Ludwig demonstrates the hypnosis effect with his secretary, she drops her revolver near the door. When Ludwig picks it up, it's several feet away, near his desk.
Continuity mistake: In Ludwig's office, when Papshmir is with him, you see a wide shot of Ludwig's desk and you can see a small remote control. When it cuts to Ludwig picking up the remote, another item appears beside the remote. (00:27:55 - 00:28:40)
Answer: Because Nordberg was working undercover in Ludwig's organization; not knowing this, the snitch would only see him working with Ludwig's crew, and would thus believe he was dirty.