I took a wrong turn on the way to the bathroom and found myself in a beautifully proportioned room I had never seen before, containing a really rather magnificent collection of chamberpots. When I went back to investigate more closely, I discovered that the room had vanished. But I must keep an eye out for it. Possibly it is only accessible at five thirty in the morning. Or it may only appear at the quarter moon - or when the seeker has an exceptionally full bladder.

They don’t need walls and water to keep the prisoners in, not when they’re trapped inside their own heads, incapable of a single cheerful thought. Most go mad within weeks - Lupin

You could be great, you know, it’s all here in your head, and Slytherin will help you on the way to greatness, no doubt about that.

The narrow path had opened up suddenly onto the edge of a great black lake. Perched atop a high mountain on the other side, its windows sparkling in the starry sky, was a vast castle with many turrets and towers.

You have to be free to fail in this world.

Mr. Moony presents his compliments to Professor Snape, and begs him to keep his abnormally large nose out of other people's business. Mr. Prongs agrees with Mr. Moony, and would like to add that Professor Snape is an ugly git. Mr. Padfoot would like to register his astonishment that an idiot like that ever became a professor. Mr. Wormtail bids Professor Snape good day, and advises him to wash his hair, the slimeball.

And sure enough, in seeking to become superhuman this foolhardy young man renders himself inhuman. The heart that he has locked away slowly shrivels and grows hair, symbolising his own descent to beasthood.