Mel Gibson’s controversial film, The Passion of the Christ, continues to steamroll its way through the top-ten list of highest grossing movies of all time, and to do so with relatively little traditional advertising. In fact, the word of mouth attached to Gibson’s feast of religious ultraviolence has been so strong that it’s changing the way some Hollywood types think about PR. With pastors, priests, and preachers around the world exhorting their followers to see the movie, this weekend’s Easter celebrations can be seen as the ultimate marketing tie-in, as Passion aims for thate loftiest of moviemaking goals: a $1 billion payday.