Continuity mistake: At the start, while the neighbourhood crowd watches Scheck make his statement at the televised press conference, when Eugene begins to sing, mailman Harvey's buttons have switched from his right side to left side on his uniform shirt. Harvey's moustache has vanished in the interim as well (his white undershirt also disappears and reappears). (00:03:25 - 00:04:40)
Continuity mistake: When the police come and suppress Blockapalooza, the letters on the police van's license plate keep disappearing and reappearing. (00:13:40)
Continuity mistake: When Helga is talking to her Arnold shrine, the candles around her constantly change position between shots. (00:22:23)
Continuity mistake: When Arnold and Gerald go to see Mr. Bailey at the Office of Information, Bailey's tie has diagonal stripes that change direction to the opposite way in some shots. (00:26:15)
Continuity mistake: When Arnold and Gerald walk out of Mr. Bailey's room, there is a door with the words, "Municipal Services" on it, which are black. When Mr. Bailey goes to talk to them, they change to yellow. (00:26:20)
Continuity mistake: When Arnold and Gerald walk out of Mr. Bailey's room, there are blinds on Mr. Bailey's window. A few seconds later, as Mr. Bailey is talking to them, they disappear. (00:26:23)
Continuity mistake: When Arnold and Gerald are standing in front of the City Morgue, there is a lantern next to the doors. In the next shot, it moves further down. (00:26:39)
Continuity mistake: When Arnold and Gerald are standing in front of the City Morgue, the design of the doors changes between shots: handles appear on the panels, extra panels appear, and the top panels become square-shaped. (00:26:42)
Continuity mistake: When the head of security carries Arnold and Gerald into Scheck's office, there is nothing on Scheck's desk. Later on, Scheck goes to his desk and picks up a glass full of cherries, which wasn't there before. (00:31:36)
Continuity mistake: When Scheck closes the doors to his office and starts talking to Arnold and Gerald, there are no locks on the doors. Then, when Arnold says, "I'm Arnold, and this is Gerald," a lock appears under the left door handle, then disappears. (00:31:41)
Continuity mistake: When Bridget shows Arnold and Gerald the equipment, there are purple binoculars on the table. In the next shot of the table, they disappear. (00:35:58)
Continuity mistake: When Bridget is presenting the equipment to Arnold and Gerald, there is a close-up of some walkie-talkies, but they are never visible on the table in any other shot. (00:36:16)
Continuity mistake: When Bridget shows Arnold and Gerald the equipment, there are purple binoculars on the table. Later on, when she shows them the watch, the binoculars are brown. (00:36:19)
Continuity mistake: When Arnold and Gerald walk to the bus stop in their suits, there is nothing next to the bus stop sign. When the bus leaves and Helga starts talking to herself, a sewer drain appears next to it for Brainy to come out of seconds later. (00:37:47)
Continuity mistake: Bridget gives the "synchronized, programmable, glow-in-the-dark watches" to Arnold and Gerald. When the two boys steal the safe's key from Nick, they wear their watches on their left wrists. Then, Arnold and Gerald get on the city bus, and thereafter for the rest of the movie, both of their watches randomly vanish and reappear during numerous successive shots, as well as mid-shot. (00:45:40)
Continuity mistake: After Scheck catches the duo in the FTI records room with safe deposit boxes, Scheck removes a painting from the wall while he rages on about the tomato incident; then he destroys the painting. However, when Arnold fights off the guard with the mustache, that painting is intact and back up on the wall in this shot. (00:51:30 - 00:51:55)
Continuity mistake: Inside the FTI records room, Scheck tells Arnold and Gerald, "My guards will now lock you away where you won't cause any more trouble." As the FTI guards approach the boys, Gerald notices the two crisscrossed cutlasses hanging on the wall, with scabbards of different colors, but when Gerald reaches for those two weapons, the two cutlasses are facing the opposite way. Additionally, the lighter scabbard tip changes color, and the hooks they hang on also change, from transparent to silver. (00:51:50)
Continuity mistake: When Murray says, "We got a neighbourhood to save," Arnold is standing on Helga's right. Then when Murray speeds up the bus, they switch places. There was not enough time for them to switch places. (01:00:24)
Continuity mistake: When Murray is told it's Mona's neighborhood that's to be demolished, he begins to speed. Murray then tells the kids to pray for the hunk of junk bus to hold together long enough to get them uptown in one piece. In the next shot, the rear right tire's hubcap flies off, but in the following shots, that hubcap is back on the rear right tire. (01:00:35)
Continuity mistake: Scheck calls Nick and informs him the kids have a copy of the document on videotape, and they're headed uptown. During the following scenes, both Nick and Big Bob have medical adhesive tape on their cheeks (due to their earlier fight). While they're outside in the neighborhood, in some shots Nick's cheek has two crisscrossed strips of tape, but in other shots only a single strip of tape; the changes go back and forth. (01:03:20)
