The concept of Time in both A Natural Death and Desperate Living.
Each song in A Natural Death exhibits Time as it occurs in the physical world, there's one song for every possible form of time.
In Hyperborea things are freezing, indicating time is slowing. In Murder blood is flowing, opposite of freezing. in Super Sapphire the line "I eat moons YET HE EATS DAYS" indicates time is measured on the very large scale of planets, compare that to the track Crickets where time is relatively tiny.
In Face Of Bear, firstly the comparison is that obviously bears are much larger than crickets and that both creatures experience time relatively different, insects live life much faster than large animals. Also he says "Winter's coming days die short at the end of autumn's reign" this indicates that time is moving backwards because the first track was winter but now its autumn, later in Kangarooster Meadows its summer time.
New York City is about the busy fast pace of a big city, or you can think of it like its exemplifying the time of evolution, cause he says "Waking up in New York City Dreaming about how it all began".
Sex Raptor, my only guess is its exemplifying any creatures biological clock. Red Tornado, fast machinery. Since time is moving backwards, I think Treasure Train is a build up to Red Tornado, like he needed the speed of the train in order to turn into Red Tornado, when he says "the sound from the windows is becoming much clearer that wind's a mirror" that could indicate he sees Red Tornado and it is him. Then the line "there's no flavor to memories and memories are moment's doom" its a weird way to describe how time is moving backwards but he's trying to move forward against it in the opposite direction. He also says "then black stars start boiling from my mouth" this is a reference to how there was a black-hole sucking the entire universe in Black Hole, and then everything was Anti-Matter in the Pizza EP, he was being Unmade.
His purple Majesty, I'm totally not sure about this one, the girl says "this time it was different", there might be some sort of hypnosis going on (wand of unyielding) or it might be some sort of repeating universe thing as described in The Greatest Weight, but both of these ideas don't fit in with my theory of all A Natural Death songs exemplifying Time in nature. OR!!! maybe this is her perspective of Sex Raptor.
In Kangarooster Meadows its summer time. I think the line in the song Desperate Living references this when he says "A play folds out on the forest floor I bought a one way ticket back to July" but I'm still not sure what it means.
In Crushing Metaphysical Crisis - "time is broken", "event horizon", "all of time unfolds".
See other post about the time concept in Desperate Living.