"A dementor." Lupin said, "One of the dementors of Azkaban."
They blink.
"Mayumi," Ginny said, rather dazed, "Why... Wha..." She paused, gathering her thoughts as she recovered from her dementor-induced panic, "How?"
"You get used to it after a while." Ron patted his sister on the shoulder, comfortingly.
Poor Professor Lupin looked so confused.