The Holy Grail: Bill Callahan’s “Smog” Dec. 10, 2001 Peel Session is a modest effort that nonetheless has much to say about both Callahan’s evolution and his consistency. This EP doesn’t rewrite history exactly, but it is revelatory about the contingent steps taken by him as an artist, more apparent in retrospect, thus amounting to a kind of rosebud explaining the move from one chapter to the next.