Continuity mistake: After it is explained that without Dave, Sam is unfocused, you see that he has dug holes just about everywhere. However, after that scene, all the holes disappear.
Some Friend - S4-E44
Plot hole: They say in this episode that Menlo was always an organized freak. But in "Principal for a Day" it turns out that he was a hyper-major kid until he started working in the school office.
Continuity mistake: In the beginning, Gretchen says she's short on money, so she can't get a chocolate milk, just a white milk. But, when T.J. walks by with his food, Gretchen has a chocolate milk, such is evident from the brown carton.
Suggested correction: Gretchen tells the lunch lady that because she is one penny short, she will swap the chocolate milk (in her hand) for a regular. She puts the milk on her tray and walks off screen. Then, when T.J. walks past her, the camera pans over to Gretchen watching T.J. with that same chocolate milk on her tray she is holding. Gretchen got distracted by T.J.'s encounter with the lunch lady and stopped to watch him, but she was still going to swap the chocolate milk for a regular later on.
Continuity mistake: When Spinelli gets the ball to play in the field behind the trees, you can see lines that would indicate that the ball was a basketball. However, when the kids are playing kickball, it's obviously a kickball.
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Bonky Fever - S4-E30
Continuity mistake: When Mikey asks the lunch lady for more pudding for Bonky and she refuses, Mikey falls down on his back and starts throwing a tantrum. A second later, he has turned 90°.
Continuity mistake: When Spinelli is challenging the hustler kid, she asks for Gretchen's bow (for a blindfold). In the shots after that, Spinelli is still blindfolded with Gretchen's bow, yet Gretchen is still wearing it.
Factual error: After Digger Dave and Digger Sam split up, they show that Sam was unfocused and was digging everywhere. Even through concrete?
Factual error: When Menlo is hoppin' scotch, he lands on 10 with both feet, and 10 is a single square.
Suggested correction: He does, but this is simply a mistake Menlo makes as a character. And it is not a 'character mistake'; I can see many people making a very simple mistake like this while playing hopscotch. I know I probably have as a kid. Also, he lands on an 8 square, not a 10 square.
Audio problem: When Randall says, "Way to hop, man." his mouth doesn't move when he says 'man' until after he's finished saying it.
Continuity mistake: In the time before King Bob tells his story about being the Prankster Prince, no one is on the jungle gym except TJ and his friends. But after Bob finishes, around 20 kids are on the jungle gym, plus TJ and co. There was not enough time for ALL those kids to get on top of the jungle gym from the time King Bob started his story to the time he finished.
The Madness of King Bob - S4-E9
Character mistake: Whenever the Hustler Kid delivers Randall's prize in the beginning, he says, "Grand prize delivery for Mr. Randall C. Weemes." But Randall's middle initial is J.
Spinelli's Masterpiece - S4-E27
Revealing mistake: When the hosepipe bursts and Spinelli's picture gets ruined, the water rises up a few inches off the ground, but the school has a chained fence so the water should run out.
Continuity mistake: Gretchen starts talking to that man who doesn't talk, but later when Mikey is singing for the first time, you see that man booing him, then a minute later Gretchen is still talking to him.
Factual error: When Gretchen is typing the pardon on Mrs. Lemon's typewriter, the paper that she is typing on doesn't go up and out of the typewriter gradually as it should. It goes up all at once when she's almost done typing.