Why, yes, keys at the wizarding school are dangerous things.  Technically the magic on them wears off within a week, so you only have to guard them paranoically during that first week, but they can still cause problems.  To counteract this, it's possible (and advised) for students to return their keys to the administration for disenchantment as soon as all three residents have utilized them; it's also possible for administrators to erase any door's memory of residents and make it start all over again.



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