Kitty smiled. Scales. Math equations. Beautiful in pure, simple ways. She understood that. "Truth, I don't really know. Or at least, not exactly. Some of it's the endless parade of bad choices in my love life and a mistake I can't undo, but some of it's more metaphysical. The nature of the soul. The persistence of memory. Whether it's ever possible to know if the friend you meet is the one you knew and whether that even matters."