Morning Becomes Entertainment - S7-E19
Continuity mistake: In the initial scene where Frasier is talking to Daphne and Roz in Cafe Nervosa, Frasier can be seen wearing a wedding ring in certain shots. (00:01:10)
Continuity mistake: When Fran's date Jack first enters the house, Fran closes the door behind him. A couple of shots later, the door is open and Fran is closing it again.
Continuity mistake: The age gap between Eric and Cory decreases as the series progresses. At the start of the show, Cory is in 6th grade and Eric is a high school sophomore, meaning they are four years apart, give or take a few months. By season 3, Cory is in 9th grade (confirmed by dialogue mentioning that Shawn, who is in the same grade as Cory, is 15 years old), and Eric is a senior, leading to an age gap of three years. The first episode of season 4 takes place a couple months after the end of season 3, with Eric and Cory returning from a summer Road Trip, but just two episodes later, Cory mentions that he is in 11th grade, while Eric is still barely out of high school, leading to an age gap of two years.
Continuity mistake: The kerosene lamp by Brisco's head disappears in the shots with the Professor kneeling beside him, but reappears in the shots of Brisco without the Professor.
Fortune Cookie / Dear John - S3-E8
Continuity mistake: When Filburt first reads his fortune cookie, it says "Bad luck and misfortune will infest your pathetic soul for all eternity". But later on when he is walking down the street it says "Bad luck and extreme misfortune will infest your pathetic soul for all eternity". (00:03:25 - 00:04:25)
When Two Worlds Collide - S5-E3
Continuity mistake: Gary has to feel around in mid air for the portal as the wall has just been bombed. But when he reaches through, later, his arm comes out of the wall which has somehow returned.
Continuity mistake: When the Warners emerge from a sealed crate on Miss Flamiel's desk and start singing, Yakko instantly appears behind Wakko and Dot as soon as the shot changes.
Used Car/Bounty Hunters - S8-E9
Continuity mistake: In "Used Car", when Beavis and Butt-head first approach the car, it's in between two trucks, a white one and a brown one. At the end, the spot where the car was is now between a green car and the white truck.
Grace and Rick and the Dance of Doom - S3-E3
Continuity mistake: The milk carton Quentin puts on the counter keeps changing position.