Continuity mistake: In the scene where Dick Shawn and all the characters find the box of money under the big W, Shawn has just thrown Jonathan Winters out of the hole so he would have room to work. But in the next five edits, Winters is both in the hole helping Shawn struggle with the box and is also shown standing outside the hole observing himself along with the others.
Continuity mistake: In the last scene when they are all on the fire escape, there is one part where the landing nearly collapses and Sylvester is seen nearly flying off the landing. The next immediate shot shows Sylvester fighting for the ladder. He apparently climbed up the landing and crawled over a bunch of people in a fraction of a second.
Continuity mistake: About three quarters into the movie, Sylvester, in his red '62 Dodge Dart convertible, sees brother-in-law Russell Finch and Mr. Hawthorne drive by in a '61 blue Chevy Impala. When Sylvester does a u-turn to give chase, you can see the passenger side of the Dart is already caved-in. A few moments later, when he rams the Dodge into the Chevy, kind of Ben-Hur chariot style, is when the initial damage should have occurred. Evidently, the chase scene was filmed out of order. Also, prior to the chase, the Dodge is shown primarily from the driver's side, perhaps to conceal the damage on the passenger side of the car.
Continuity mistake: In the scene near the end when everyone piles into the two cabs, Mr. Pike is refused entry a few times, but finally squeezes in on the left side. When the camera cuts to inside the cab, he is second from the right. There is no way he could have slid past Sylvester and the English guy.
Revealing mistake: The blue Willys (Jeep) station wagon used for the blue-screen shots was a two wheel drive version. During the argument shortly before the crash, the Englishman driver abruptly shifts gears, revealing the three-on-the-tree shifter on the steering column, used only on 2WD versions. The on-location filming used the 4WD version, with the logos visible on the tailgate and side of the hood. Also, the distinct 4WD front axle can be seen in many shots.
Revealing mistake: Whenever a back projected shot is used the cars are supposedly driving at top speeds yet no-ones hair, hat, scarf etc ruffles in the wind. In fact there's no evidence of movement whatsoever. This is particularly noticeable in the scene where they are all crammed in the truck and one guy is leaning over the side shouting at drivers.
Character mistake: When Spencer Tracy is talking to his wife and daughter on two separate telephones, he places the phones up against each other so mom and daughter can talk to each other. One phone should be upside down so it would be speaker to transmitter rather than speaker to speaker.William Bergquist
Revealing mistake: Watch the firetruck ladder as it sways. During the long shots showing the entire ladder, it is swaying from ground level. During close-ups, the apparent pivot point is just off the bottom of the screen, indicating a much shorter ladder was in use.
Continuity mistake: The two taxis collide and get dented when turning around at the Captain's house. During the subsequent chase, the damage has disappeared.
Revealing mistake: At the end when the police officer crashes through the window of the pet store and all the dogs are licking him, it is extremely obvious that it is short piece of footage being rewound and played over and over again to extend the length of the shot.