"You don't know if it's happened before or you don't know if I should get Newt?" Sirius asks because, in this moment, he really isn't honestly certain exactly what Kieren can remember and what he can't. He's explained that it's a brain thing, that the drugs aren't enabling him to create new memories, but does that mean the drug could ever reverse entirely?

If this were a spell he might have some idea of what to do, but this Muggle science is boggling.

He glances down at Kieren's nose again, frown deepening. "What if you don't stop bleeding? What does that mean?"