You, Harry, Hermione and Ron had to sit in a cabin with one other since all the others were full. That other person was the new Defence Against The Dark Arts teacher, Professor R.J Lupin with a blanket draped over him, sleeping

Ron: "Who's that?"

Hermione: "Professor R.J Lupin."

she said, reading off his briefcase. But of course, Ron didn't see that.

Ron: "Do you know everything?"

she rolled her eyes, pointing at his briefcase

Hermione: "It says it on his briefcase."

Ron: ".. Oh."

You, Harry and Hermione giggle quietly as to not wake Lupin. Then suddenly, the train stops and everything freezes over. The windows, the glass of water, and Ron's handprint from putting it on the window. And then a hand approaches, slowly opening the door. It was a dementor.