Audio commentaries are not always the best sources for information or for critical analysis. Sometimes the filmmakers providing the commentary are just going through the motions, probably fulfilling some contractual obligation. In other instances, these tracks merely dish up some fun factoids or anecdotes, but shy away from any incisive let alone critical commentary.
William Friedkin’s commentary track on the “25th Anniversary Special Edition” DVD for The Exorcist is very insightful, especially when he discusses motifs. Visual and narrative motifs are commonplace, but the director of this horror classic talks about how other elements can also be used to create such meaningful recurrences. This short clip mentions how the filmmakers used a specific character’s entrances into each scene as a motif, setting up a pay-off at the end of the film.