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). In some shots Nick's cheek has two crisscrossed tape strips, but in other shots only a single strip of tape; the changes go back and forth. (01:03:20)
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: 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: 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 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)
Other mistake: While Arnold and Gerald are headed to FTI on the city bus, Murray tells them about Mona. When Murray says, "You meet a girl, you think it's forever," the animation is a bit skewed, as it shows the steering column going through Murray's right thigh. (00:46:25)
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: At the start, while the neighborhood 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)
Other mistake: In the FTI records room, when Arnold and Gerald open safe deposit box 999, the box is quite empty with a mirrored surface, and we can see the reflection of Scheck appearing behind them. The problem is Scheck's reflection is not backwards. (00:50:50)
Other mistake: When Helga kisses Arnold on top of the FTI building, Arnold's hat falls off his head, but you can see another hat on his head as the other one is falling. (00:58:02)
Other mistake: When Bob and Nick start fighting, Nick runs into the kitchen and grabs an egg beater. Right before he tries to attack Bob with it, his right shoulder is drawn incorrectly. (00:49:32)
Revealing mistake: When Helga tells Arnold that she likes him a lot, as Arnold says, "You do? You did this for me?", his mouth disappears for one frame. This is easier to see in slow motion, but it's still visible at normal speed. (00:57:26)
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 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)
Other mistake: When Bridget tells Arnold and Gerald, "If you're gonna try and save the neighbourhood, you're gonna need some equipment," Arnold's right eye duplicates. (00:35:55)
Continuity mistake: When Bridget uses her zip line, Helga's arms are folded, and Gerald is standing next to her. In the next shot, her arms are down, and Gerald is standing next to Arnold. (01:07:19)
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 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 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)
