"The song titles are complex, but when it comes to the album titles, they lay them out like IKEA instructions: Zeppelin I, Zeppelin II, Zeppelin III, Zeppelin IV. The fifth album, Houses of the Holy, is where they regain their insanity. Just to fuck with you, it does not contain one of their few hits that has the title in the lyrics, "Houses of the Holy". That's on Physical Graffiti."