"Yes. Transferring people from one body to another is not something we do a lot of around here. Can't say that I've heard of another case, in fact, unless you count what happens to vampires."
"Oh, we lose our souls. Replaced by some sort of demon spirit, is I think the going theory. We keep all the same memories, but our personalities change, usually not in nice ways."
"Huh. Memories and souls are attached for us, we don't have Book's memories still now that his soul's in Lightning's body."
"It might be that the relevant thing in each case is a different thing, and they're only getting the same word because of limited vocabulary. Or perhaps your world has a different sort of soul. I wonder what would happen if your sort of person became a vampire?"
"I don't know, but we don't want to try it. We have been eaten by demons enough. We wouldn't be a good test case anyway since we're unusual."
Sherlock giggles. "I won't suggest that you experiment, then. Does the cage full of mice serve some sleep-related function?"
"Yeah. Trading off cohabitors fixes mental tiredness but not physical tiredness, so the mice take that. They're good if we have an injury or get sick, too. I could use more, a bunch of ours died when we killed the first demon we met. Then - the one with the - portal face."
"You don't, strictly speaking, need sleep-mice around here. But I could look for some, I suppose."
"Sleeping seems like such a waste of time. And we do still have to share."
"I'd be more inclined to agree if vampires didn't catch fire in sunlight. Rather limits what I can do during the day. Sleeping is a nice alternative to boredom."
"You'd have a much harder time where we're from," she says. "There's usually at least one sun around. But we can stay awake and think at each other, and this book is turning itself into a Nlaaki-to-English textbook as we speak."
"It loses its content eventually, but the more of it there is, the longer it takes to fade," he says. "As I understand it. The book is not technically mine, I just happened to know it was here."
"Good question. We could always try asking. Well, you could; I have to be back home by sunrise, and the owner of the book is not likely to show up until well after that."
"The librarian in charge of this library, I believe. Many of the books belong to the school, but a lot of the good magic-related ones are his. I've never met him, but I've gone through his desk a few times. He seems nice enough."
"The kind that teaches a lot of largely unwilling teenagers things that they don't especially want to know."
"Oh, that kind. We got out of that a while ago. Book's still in school, but on purpose."