It's classically insane stuff, with "Yes we can" becoming a polite "Thank you Satan". There's a Lovecraftian surrealism with lines like "Sub-Earth - the mark that's now sooner". Don't miss the revelation of the Greek/Egyptian/posthumanist axis in "Hear my composite self for the Pharoah Zeus."
I still think it was The Exorcist (1973) which kicked off the great wave of backmasking madness, with that terrific "IAMNOONE" scene.
(thanks to gimlet-eyed Jesse Walker)