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.
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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