I'm kind of surprised that I haven't seen reference to the piece of paper that drops from above (offscreen) onto the TARDIS console right before the cut to next week's preview. If I missed reference to it here or in another thread, my apologies.
Any wild speculation? Note from the TARDIS? Perhaps the TARDIS dropping a page ripped from the History of the Time War (the one referencing the Doctor's name) so that Clara won't find it again?