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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