" Do all people have that? A face, a phrase, a landscape, an air bubble from the past suddenly floating up as if released by the head warden's child from a cell in the brain while the mind is at work on some totally different matter? Something of the sort also occurs just before falling asleep when what you think you are thinking is not at all what you think. Or two parallel passenger trains of thought, one overtaking the other. "

― Vladimir Nabokov , Bend Sinister