Continuity mistake: During the musical number "Somewhere Only We Know", you can see Brittany step down from the stairs in the background as The Warblers circle around Kurt and pat him on the shoulder. The next shot shows her stepping down again.
Prom Queen - S2-E20
Continuity mistake: When Blaine and Kurt are in Breadstix talking about Prom, the amount of soda in both of their glasses changes between shots.
Prom Queen - S2-E20
Continuity mistake: As Kurt and Dave are talking in front of Kurt's French class, a short girl with a brown ponytail enters the class twice.
Continuity mistake: Near the end of the episode, when Mr Schue is talking to Terri in the school hallway, there are several people walking around in the background and there is even one student running towards the camera. In the next shot - one second later - the hallway is completely empty.
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: 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.
Continuity mistake: Kurt informs Blaine that he flew in an airplane for The First Time. This however is incorrect, as Kurt flew to Albuquerque NM for the 2010 Cheerios Championships. In the season 1 episode Sectionals it is mentioned the Cheerios Nationals are in Albuquerque and in the season 1 episode Funk The Cheerios return from Albuquerque the same day. 1500 miles in less than a day means they flew.
Continuity mistake: Near the end when Brittany is talking to Santana outside their lockers, Brittany's fringe keeps changing between shots from across her forehead to down the side of her ear every time the camera switches from facing her to facing Santana.
Continuity mistake: At the end of the episode when Kurt and Blaine are sat in the Lima Bean, the position of Blaine's hand where it props up his face changes. Whenever we see Blaine from the front, his fingers are curved slightly, but when we see Kurt (and the back of Blaine's head), his fingers are held straight so they do not interfere with the shot.
Continuity mistake: Puckerman is on a skateboard and then jumps on to the bench, but the skateboard just disappears.
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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