Factual error: The wedding is at a Christian church performed by a Christian minister, but at a Christian wedding the groom stands on the Minister's left side and the bride on his right. The way Will waits for Emma is the way that the bridal party stands at a Jewish wedding.
Continuity mistake: Just as Kurt is pulling up a chair next to Blaine in the Lima Bean scene, Blaine's arm is down by his side. Yet when Kurt hooks their arms together in the next shot, his arm is on the table.
Deliberate mistake: When Howard enters Figgins' password to hack into his AOL account, Figgins' inbox is obviously visible behind the login box, which simply disappears once the password has been entered. In addition, look closely at the inbox and you'll see that not only is there no mail, they are actually in GMail (the logo has simply been edited out of the top corner).
Continuity mistake: When Rachel and Ms. Corcoron sing "Poker Face", near the end they switch places between shots.
Big Brother - S3-E15
Character mistake: During "Somebody That I Used to Know," Blaine puts down his satchel. At the end of the song, he leaves the auditorium without picking it back up.
Continuity mistake: While Santana is singing "Back to Black", Jessie is seen obviously scribbling something down. Yet at the end, his notepad is shown with a drawing of a cat upon it. If he was drawing the cat, he would have been drawing smooth lines, not scribbles, as the drawing contains no scribbles at all.
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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