Continuity mistake: During "Bad Reputation", as the kids are singing "Ice Ice Baby", their sheets of music continually change position, especially with the people sitting down. For example, in the first shot Mercedes is holding her music in her right hand. In the next shot it's down on her lap. In the third shot she's holding it with both hands, and in the last shot it's in her right hand again.
Laryngitis - S1-E18
Continuity mistake: During "Laryngitis", Puck pulls Mercedes up to come sing "Lady is a Tramp" with him. Yet in the very next shot, just as she starts singing, she stands up again. So she stood up twice.
Laryngitis - S1-E18
Continuity mistake: During the "Lady is a Tramp" number, Puck puts on a hat with the front of the brim flipped down. The brim miraculously flips up and back down throughout the scene.
Continuity mistake: When Artie tries to walk with crutches after the "step dance" practice with Tina, he falls down violently. Immediately after the fall, the crutch is still attached to his left arm, which is angled away from his body. In the very next shot, the crutch is almost a foot away from his arm, which lies now at a different angle. (00:10:05)
Continuity mistake: During "Theatricality", when the boys are singing "Beth", just as Puck sings "Me and the boys are Playin'" for The First Time, Finn is visible sitting behind Quinn. Yet Finn went to sit down and sing with Puck and is obviously sitting with the boys in the next wide shot.
Continuity mistake: When Rachel and Ms. Corcoron sing "Poker Face", near the end they switch places between shots.
Continuity mistake: During "Blame It on the Alcohol", when Quinn is shouting at Puck, her hair is messy and straight. Yet a little while after, during "Don't You Want Me", her hair is curly and styled perfectly.
Continuity mistake: During "Grilled Cheesus", the grilled cheese sandwich with the face of Jesus changes occasionally between shots. Sometimes the burn is slightly darker, or the edge is changed.
The Rocky Horror Glee Show - S2-E5
Continuity mistake: When the kids are practising the 'Dammit Janet' song, Finn draws a heart on the whiteboard in the back of the choir room. The shape of the heart changes with almost every shot it is in.
Continuity mistake: During "Never Been Kissed", just after Sue activates the confetti cannons and is talking to Will, the amount of confetti on Will's shoulders changes between shots.
Continuity mistake: During season 2 "Never Been Kissed", just as the Warblers begin to sing "Teenage Dream", a boy with a briefcase walks in front of Kurt, heading towards the left. Two shots later, the same boy with the breifcase walks left in front of him again.
Continuity mistake: While the Warblers are singing "Teenage Dream", during the closeups of Kurt, his bag's strap is under his jacket's lapel, but in the long shots, it's on top of the lapel.
Continuity mistake: Puck butters the floor, and as Kurt slips and falls, The Substitute is not where she had been standing. The next shot, she's still there. (00:07:45)
Continuity mistake: In the "Singing In the Rain" dance, the second time the three guys are on their knees, they splash water with their hands. The third time they splash, the water drops are moving toward the stage instead of away. And the rain in the background is falling up.
Continuity mistake: When Sue and her mother are singing "Ohio", during the closeups, Sue has her arm around her mother's waist, yet in the wide shots, Sue's arm is hanging by her side.
Continuity mistake: During Season 2, Episode 9 (Special Education), just as Blaine is singing "Hey soul sister, I don't wanna miss." for the last time, he is several feet in front of the other Warblers. But during the next shot, as he is singing ".a single thing you do.", he's right in front of them. So he jumped back several feet between two shots.
The Sue Sylvester Shuffle - S2-E11
Continuity mistake: When the Warblers are singing "Bills, Bills, Bills", one of them throws the sheets of music up in the air as he spins. For the remainder of the song, the sheets are on the floor during some shots, but have disappeared in others.
Continuity mistake: When Lauren drags Puck into the storage closet for Seven Minutes In Heaven, there are hearts on the wall which appear to be decorations for Valentine's Day. As the Seven Minutes In Heaven happened prior to Sectionals, which was well before Valentine's Day, these shouldn't be there.
Continuity mistake: During Mike's "Bubble Toes" dance number, the chain on his pocket watch switches between being over a foot long, swinging about as he dances, and being only a few inches long. (00:25:40)
Answer: The show is purposefully stylized and over the top. It is not designed to be an accurate, realistic representation of American high school. The idea that the glee club is so unpopular other students can literally throw garbage at them with impunity is an over-exaggeration of how glee club is considered "un-cool" compared to things like football. However, there is a second way of looking at it. The audience is simply never shown anyone getting into any trouble for throwing slushies. Just because we don't see it doesn't mean it never happened.
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