So I'm doing a complete re-read in preparation for TGO, catching up on the Slog group re-read on this board as I go. I'm about halfway through TTT, and something keeps bugging me (and I don't think it's been addressed in the books).

Question: WTF is the deal with Kellhus's halos? Mass delusion? Actual encroachment of the Outside created by the force of others' belief in the Warrior-Prophet? Or just a cheap parlor trick typically used to entertain Dunyain children at birthday parties?