Neville Longbottom's Remembrall turns red because he is the only student who forgot to put on his black school robe.
Film/Series: Harry Potter and the Philosopher's Stone
Category: Prop Costume
Timestamp: 00:58:15
When Neville receives a Remembrall in the Great Hall, the smoke inside turns red, indicating he has forgotten something. While he nervously states he can't remember what he forgot, observant viewers can see the answer hidden in the costume design. Every other student sitting at the Gryffindor table is wearing their black Hogwarts robe, except for Neville, who is only wearing his grey sweater.
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