Save The Tree / New Teacher - S2-E1
Continuity mistake: In New Teacher when the principal is telling the class about their new teacher the students switch seats between shots.
Olga Comes Home / Sally's Comet - S1-E15
Continuity mistake: In Sally's Comet when Gerald, Arnold, and Grandpa are in the traffic jam on the way to Hawk Mountain the position and type of cars around them change. When we first see the car there is a truck there and no room for them to turn around. When they do turn around then there is room and the truck is gone.
Continuity mistake: The pets OK sign on Arnold's house changes in different episodes.
Continuity mistake: When Helga is talking about Arnold, the computer store she is in front of is on a corner (Phoebe is seen going around the corner) but a few shots later the store is no longer on a corner.
The List/Haunted Train - S1-E8
Continuity mistake: At the beginning of The Haunted Train Grandpa's ice cream changes color from orange to white.
Helga's Locket / Sid and Germs - S5-E7
Continuity mistake: When Sid decides to be a slob again, he picks up his frog and you can see that he has gloves on. When the following shot shows a close-up of the frog in Sid's hand, the hand holding the frog does not have gloves on.
Parents Day - S5-E6
Continuity mistake: In the tricycle section of the last event, the chinpiece of Helga's helmet keeps switching colors.
It Girl / Deconstructing Arnold - S4-E9
Continuity mistake: When Eugene breaks into the area with the dogs, you see the pedals of his bike tossed into the air, but the pedals fell off on the other side of the street.
Career Day / Hey Harold! - S3-E11
Continuity mistake: There are more than 16 slips in the hat, but only 16 students in class, and only 12 hands went in to pull out slips.
Big Gino / Jamie O. In Love - S4-E2
Continuity mistake: During "Jamie O. in Love," in the very last scene, Jamie drives up in a car whose front license plate reads "Killer." When they leave, the back license plate reads "Killr." There is no space for a letter to have possibly fallen out (not that a letter can fall off of a license plate).
Steely Phil / Quantity Time - S2-E12
Continuity mistake: Chinese Checkers is supposed to be with ten pieces per side, not six.
Freeze Frame / Phoebe Cheats - S2-E8
Continuity mistake: The next night, Phoebe's bed clothes switch back and forth between her nightgown and her dress.
Continuity mistake: Ms. Perfect: When Lila is wearing her new blue outfit at recess, she wears light blue bows in her braids, but when she is shown in close-up, she is wearing her regular green bows. There is also a small animation glitch with Lila's right bow. (00:15:22)
Arnold Visits Arnie / Chocolate Boy - S5-E12
Continuity mistake: Arnold Visits Arnie: When Arnold walks out of the movie theatre, he walks into Hilda and they fall over. In the next shot, they turn 90° counterclockwise. (00:06:45)
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 first shown in the laundry room, the latch on the washing machine door is missing. In the next shot, the washing machine and the dryer switch places, and in the shot after that, the latch is back on the washing machine door. (00:21:10)
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)
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)
Answer: The episode doesn't really elaborate on who the kid was and what his motives were, so its pure speculation as to why he took it. Perhaps the kid could simply want a ball all for himself and decided to just take it, or was simply a rotten kid. The truth is the kid's motives are not important to the story other than it highlights Arnold was having a lot of trouble getting through the list.
Lummie ★