Continuity mistake: During the scene when Wally gets hit by the soldier in the cafe, and Wally bumps into another soldier, causing him to go into a cake, take notice of how much cake is on him throughout the different camera shots. Also Pops (the owner) starts to wipe the cake off of the soldier's face. The amount of cake changes between shots. (00:09:20 - 00:10:15)
Continuity mistake: When the Army knocks a hole into the front door of the Douglas home with the anti-aircraft gun barrel, notice that the position of the hole changes between shots. And when the soldiers pick the door off of Mrs. Douglas you do not see the hole. Also notice that the door is standing back up and intact, in the background, as the soldier explains to the Douglas family about the gun. (00:29:30)
Continuity mistake: Before Ward puts the ammo in the cannon, when Wood greets Mrs. Douglas the string to pull the blind changes length back and forth depending on the angle. (01:28:50)
Continuity mistake: As the two look-outs get on the big wheel the thin guy with the ventriloquist's dummy sits on the right. But later in the film he is on the left.
Revealing mistake: When the Ferris Wheel at the theme park has broken from its mounting and is rolling down the pier, it appears to be rolling forward but rotating anti-clockwise when if it is rolling forward it should be rotating clockwise.
Plot hole: When Ward's son hits the switch marked "Do Not Touch This Switch", every light in the amusement park comes on, music starts playing, and the rides all start moving. It's a funny gag, but it seems unlikely that one switch would power every single thing in the amusement park, and that everything in the park has been left on "full speed." If that's the case, when Angelo first sent the two lookouts to the top of the ferris wheel, everything else in the park should have come on then too.
Factual error: When John Belushi, Wendy-Jo Sperber and Treat Williams are on the stolen motorcycle, Belushi gets mad, pulls a pin, and disconnects the sidecar from the motorcycle. This is not how sidecars are actually attached or they wouldn't go the same direction as the bike.
Revealing mistake: The Douglas' house which falls off the cliff at the end of the film was built to do just that. It was only used for exterior shots, and the interiors were filmed on a sound stage. If you watch carefully as the house crashes, you can see that it has no interior.
Factual error: In the beginning, a submarine surfaces. The area is supposed to be off the coast of California. A large rock is seen which is obviously Haystack Rock, a tourist destination off the coast of Pacific City, Oregon.
Revealing mistake: The actor who played "Wally" did all of his own dancing during the big dance scene, except the part where he tap-dances down the long table of food. We see Wally jump up onto one end of the table, then the shot cuts to a close-up of his feet as he tap dances among the plates and glasses. When he reaches the end, he jumps up into the air and drops into frame, showing that it's really him. Since the actor couldn't tap dance, the film's choreographer did the tap dancing part. At the end of the table they hung a trapeze bar and the actor hung from it with his feet pulled up. When the choreographer reached the end of the table, he jumped up into the air and grabbed the bar just as the actor let go, so it looks like the same person. But if you look very carefully, you can see the actor's shoes dangling above the edge of the table just before the choreographer jumps.
Visible crew/equipment: When Wild Bill crash lands his P-40 Tomahawk in the street, then dazedly tries to "bail out", watch his parachute. A nearby explosion is supposed to catch the parachute and pull him backwards, but the 'chute doesn't react to the explosion. Instead, a line attached to the end of it pulls Wild Bill backwards.
Revealing mistake: When the tank runs over a car during the riot scene, you can see that the car has no engine.
Revealing mistake: During the riot scene, "Stretch" drags Betty under a truck so he can rape her. Wally drives the tank across the street and bumps the truck, knocking it over (so he can save Betty). If you watch, the tank bumps the truck, there's a pause, and then the truck flips over. It is obviously pulled over by something off-screen and not by the tank.
Factual error: When Frank Mcrae and John Candy are arguing in the tank, Candy gets covered in soot when the exhaust manifold blows. This couldn't have happened as the engine in the tank is in the rear of the vehicle and it's separated from the crew.
Deliberate mistake: When Betty falls in the traphole, Maxine is right behind her, yet when the angle changes she's not only in front, but has turned 180ยบ. This allows for a funnier gag, but is still a mistake.
Deliberate mistake: Though the loose ferris wheel keeps rolling for over a mile, the guys seated on it remain in the same position all the time instead of rolling down and getting crushed by it. Furthermore, they disappear in the wide shots and the wheel appears empty.
Continuity mistake: When Ward's tank rampages through his home's front door, strangely enough there are two exact angles of it, one right after the other. On the first, the door falls down, but the next time it's dragged several meters ahead.
Revealing mistake: When the swimmer is lifted by the periscope she is wearing skin coloured underwear around her thighs, despite she is supposed to be naked.
Other mistake: The chandelier falls at the crystal ballroom and Wally drops. You can see he's nowhere near it but he still falls down.
Continuity mistake: When Captain Loomis shows up in Barstow, he gets out of the vehicle and its lights are on. When he's standing in front of the car and we see him from behind, the lights are off. They are then on again when he gets fired on.
