"Motive's the trickiest part of the equation, and unless somebody very obviously tips their hand, I'm thinking it's probably the least likely to be answered anytime soon." Not that we've got much to go on with any part of the equation in question, but at least the how can have scientific theory applied to it. The why is a lot more tricky.

"You understand planetary physics," I continue with a motion Nerys' way. "For the people who don't, it's easier to buy that the sun started moving the wrong direction in the sky, but you and I and a few others know we wouldn't still be alive if that had actually happened."