Full Moon / Student Teacher - S4-E1
Revealing mistake: Full Moon: When Harold tells Arnold, "Remember when I said you didn't have any guts because you wouldn't moon Principal Wartz?" his mouth briefly disappears. This is easier to see in slow motion but is still visible at normal speed. (00:11:16)
Love and Cheese / Weighing Harold - S4-E7
Continuity mistake: Love and Cheese: When Arnold is trying to knock the bottles down and Lila gives him a flirty look, her collar turns green for one frame. (00:06:12)
Continuity mistake: Ms. Perfect: When the flap on Lila's table falls down, her lunch bag falls over. When the tray of spinach and fish falls on her, it changes position. (00:18:37)
The Aptitude Test / Oskar Gets a Job - S3-E9
Continuity mistake: Oskar Gets a Job: When Arnold and Suzie are in the laundry room, Suzie says that she wishes Oskar would do what he says he's going to do. In the next shot, the washing machine and the dryer switch places. (00:21:10)
School Play - S3-E19
Other mistake: After Helga gets mad at Arnold in the beginning, as Helga says, "What an annoying little smarty pants know-it-all," the lunch lady's body is invisible through the glass on the counter, leaving only her upper half visible. (00:01:12)
Phoebe Takes the Fall / The Pig War - S3-E16
Revealing mistake: Phoebe Takes the Fall: When Phoebe is in Helga's room helping her study for the tournament, as Helga says, "Well, let's call it a night," her left side hair is missing, then it appears mid-shot. (00:06:54)
Love and Cheese / Weighing Harold - S4-E7
Continuity mistake: Weighing Harold: When Arnold shows Harold his reflection in the water, the reflection of his tooth is not reversed, it is on the same side of his mouth. The second time his reflection is shown, it is reversed. (00:16:37)
Career Day / Hey Harold! - S3-E11
Other mistake: Hey Harold!: When Harold's family is talking about Patty during dinner, as Harold's mother says, "We can show her those adorable baby pictures of you," her left eyelid is not colored in. (00:20:39)
Career Day / Hey Harold! - S3-E11
Other mistake: Hey Harold!: When Harold and Patty are dancing together, as Harold says, "They said I didn't apply myself," Patty blinks twice, and her right eyelid is not colored in. (00:17:00)
Door #16 / Arnold as Cupid - S1-E10
Other mistake: Arnold as Cupid: When Oskar gives Arnold breakfast, besides the fact that the objects move from the left side of the tray to the right between shots, look at the glass of orange juice as Oskar lowers the tray to Arnold. Despite Oskar never rotating the tray around, the glass of orange juice glides itself over to the top left corner of the tray. Very weird. (00:14:34)
Arnold & Lila / Grand Prix - S3-E13
Continuity mistake: Arnold and Lila: On the bus, when Arnold tells Lila that he doesn't like her like her, Lila is smiling at him. In the next shot, she is suddenly frowning. (00:07:01)
Runaway Float / Partners - S2-E20
Continuity mistake: Runaway Float: When Arnold first sees the beeper float, he says, "How can they control that thing?", and Gerald is sitting on the curb to the right of Arnold. In the next shot, Gerald is suddenly behind him. Arnold is also a lot further away from the curb than he originally was. (00:08:16)
Arnold Betrays Iggy / Helga and the Nanny - S3-E10
Revealing mistake: Helga and the Nanny: When Helga tells the other kids that her nanny was fired, as she says, "Yeah, well my dad found his lucky belt under her bed this morning," her left-side hair disappears for one frame. (00:20:06)
Runaway Float / Partners - S2-E20
Revealing mistake: Runaway Float: When Arnold and Gerald are watching the parade, Arnold turns his head to look at the marching band. When he looks away from it, his left eye doesn't move, and it stays visible in his hair for the remainder of the shot. (00:07:51)
The Aptitude Test / Oskar Gets a Job - S3-E9
Revealing mistake: The test paper Eugene put back in Harold's folder is blank.
Suggested correction: The paper is not blank. Helga used a purple pen to fill in her paper, and Eugene put it in Harold's folder. The paper is filled with purple ink.
Arnold's Room / Helga vs. Big Patty - S3-E4
Continuity mistake: In the locker room, Sid's hair goes from stringy to full and back to stringy.
Eating Contest / Rhonda's Glasses - S2-E13
Continuity mistake: In the last scene, Rhonda is seen through the bus's rear window as sitting in the back of the bus - but just before that, she's talking to the girl with the frizzy hair in a seat closer to the front.
