Other mistake: When Cory and Shawn are auditioning for "Guys" and they're talking about the first person they pick, Cory says,"He's shorter than me and..." but after they pick both guys and he's talking to them, you can see that Cory is the shorter one.
Other mistake: A lot of times in scenes in episodes taking place in high school, characters are shown walking up to their lockers and opening them without putting in the combination first.
Other mistake: When anybody leaves the house, you can always see that when they open the door, they turn left and go; you can also see bricks/part of a porch in front of the door. But when the house is shown from the front, the fences are on both sides of the door, but not in front of it. So there is no way that they could turn left when leaving.
It's a Wonderful Night - S1-E18
Other mistake: When Eric is ordered to go to his room he mentions that Feeny used to be his 6th grade teacher. However, later in the series it is emphasized several times that Mr. Feeny was Cory's teacher every grade he was ever in. With Cory only being 3 years younger than Eric, it would not be possible for Feeny to have been Eric's 6th grade teacher as Cory would have been in 3rd grade and had Feeny as a teacher per what is stressed on multiple occasions later in the series.
Other mistake: At the beginning of the episode, Eric talks about how Alan's Navy background will cause him to use any means necessary including torture to find out about his birthday party. Cory chimes in and states that Alan was a cook in the Coast Guard. The plot of the Season 1 episode Kid Gloves concerned a necklace Alan gave Cory for his birthday, which Alan himself earned for placing second in his weight class for boxing in the entire Navy. So either Cory doesn't correctly remember his own father's military background, or the show needlessly retconned it. (00:00:43)
For Love and Apartments - S7-E2
Other mistake: When Cory is trying to get Topanga's parents to reconcile, Topanga's mother mentions to her ex-husband about the "beautiful child they've made." Given that she says "child" in the singular, this can only refer to Topanga. However, the season 1 episode She Loves Me, She Loves Me Not established that Topanga had an older sister named Nebula. So the mistake is that either the show is acting like a character that was firmly established never existed, or Topanga's mother doesn't realise she has at least two children. (00:15:32)
The Eskimo - S5-E13
Other mistake: When Shawn is saying "Thanks a lot Topanga" after she falls to the floor, he is looking down directly in front of him, but she is to his left.
A Very Topanga Christmas - S5-E11
Other mistake: When Topanga knocks on Cory's door at 3:00 AM, he comes out and expresses that he's always asleep at this time of night. Despite this, he shows no signs of having just been awakened from his sleep. On the contrary, he appears very alert.
Other mistake: When Cory throws the CD out of his bedroom window, if you listen closely, you can hear the CD land in a soft terrain. However, the next day at school, Mr. Feeny pulls the CD out of his suit pocket and says that it sailed through his living room window and landed on his walnut credenza. If the CD managed to make all the way into Feeny's house, then the sound of it landing would not be audible.
The Heart is a Lonely Hunter - S3-E15
Other mistake: Dana exits Chubbie's and sees Shawn has set up a picnic for her. She remarks that it's the middle of winter and Shawn is shaking from the cold, but her breath is not visible.
Other mistake: When Cory goes into the apartment and starts to film Shawn and Jack fighting, he is sitting on the coffee table behind them. When what Cory is filming is shown, the camera is facing their sides, not their back. (00:10:47 - 00:11:11)
Other mistake: After Jack and Rachel tell everyone they broke up and Angela says to Shawn "Friends, okay?", the camera is noticeably out of focus and then comes into focus when Shawn says "Hate you or love you..." (00:05:10)
Other mistake: Early in the episode, Amy mentions that she is 7 1/2 months pregnant. This episode takes place around Valentine's Day, which means she would have become pregnant at either the end of June or the beginning of July. However, she revealed she was pregnant around the time Cory, Shawn and Topanga had their senior prom, which would have been around the end of May or beginning of June at the latest, prior to their high school Graduation. So she should be around 8 1/2 months pregnant at the least.
Other mistake: When Mr. Feeny is telling the story about Topanga and Cory in the first grade, he mentions that Shawn told him to leave them alone. However, the season 3 episode "City Slackers" established that Shawn wasn't in school with Cory and Topanga until he was around 12, and that he was in and out of 5 schools in different states before then. (00:18:40)
Other mistake: As Wendy is leaving the apartment, she writes her phone number on Shawn's palm and tells him to call her. She only scribbled a few lines on his palm for a second, not nearly enough time to write her entire phone number down.
Other mistake: When Eric and the other security guard discover Mr. Feeny entering the school, Feeny expresses that Eric snuck up on him. Eric was five feet away from Feeny when he first saw him, and was also talking loudly when making his approach towards him. There's no way Feeny couldn't have heard him.
Other mistake: When Eric asks Mr. Williams why everyone is applauding Frankie missing a shot in their game of pool, Mr. Williams notes it's because no-one has ever seen two people play for three hours without sinking a shot. However, if you rewatch a couple of times the part where Frankie takes his shot and you count the balls on the table, there are only 14, not including the cue ball, when there should be fifteen. If by chance a ball was knocked off the table, then given how much the crowd was into the game, someone would have told them they needed to place the ball back on the table.
The Pink Flamingo Kid - S3-E17
Other mistake: When Eddie busts Cory filming him and his cronies, he spends a few moments intimidating Cory before snatching the camera out of his hands and throwing it against the ground. After Shawn breaks up the situation and notes that they broke the camera, Cory remarks that they didn't get the tape and proceeds to pull a tape from under his jacket. Cory's hands are both visible gripping the camera the entire time that Eddie is confronting him, and he didn't have the opportunity to retrieve the tape when Shawn intervened, so he couldn't have had the tape tucked away.
Other mistake: Eric is showing Feeny the doll he has and pulls the string to make it talk. When he makes the doll do mission impossible, he pulls the string but the doll doesn't say anything. (00:03:47)
Chosen answer: In the present day, with the United States abiding by more stricter school health laws, for the most part this wouldn't be in school cafeterias as many cannot even have carbonated beverage machines now. However, in the 90s when the show takes place, it wasn't unheard of for there to be coffee machines in the cafeteria of small schools where the teachers eat with the students as we see them do often in the show. The idea being that the cafeteria was small enough so a teacher or hall monitor could catch a student before they could drink the coffee.