Who is the giant three-headed dog that guards the trapdoor leading to the Philosopher's Stone in the first book?
Fluffy
<s>[INST] <<SYS>> Answer as briefly as you can to the following question. You are required to give a one-shot answer: <</SYS>> Who is the giant three-headed dog that guards the trapdoor leading to the Philosopher's Stone in the first book? [/INST] Fluffy </s>