Carnival of Souls is very subterranean, going underneath our merely verbal senses. The plot is of little importance, but atmosphere is everything. The eerie music, strange people and oddly shot black and white scenes grab at our fears of loneliness and death. You know (but more importantly, feel) that Mary is inexorably doomed. The effect is powerful because it succeeds in making Mary a proxy for ourselves. The effects are subtle, not depending on "special effects" in the usual sense. Rather, they rely on creative use of camera composition, restrained acting (where less is more), and hauntingly strange music.