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.
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.
Revealing 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: 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.
Revealing mistake: In the chase scene, Milton Berle and Terry Thomas are actually driving two different blue '61 Chevrolets. Initially, they are in a rare Super Sport as evidenced by the crossed flags emblem on the rear seat speaker cover. Fortunately, the car they eventually crashed was the less desireable non-SS version (i.e. no crossed flags emblem present). (01:40:05 - 01:47:25)