Come in Number 51, Your Time Is Up Lyrics

you'd be surprised what changing a key can do...

err, does this song even exist?

Yes, Vannaroth, it Exists. It is on the Zabriskie Point soundtrack (with a few other Floyd tunes). 'Number 51' is a studio version of 'Careful With That Ax, Eugene'. (Less heavy than on Ummagumma, but more creepy, and more keyboards).

Apparently, this song is Careful With That Aze, Eugene in E minor (instead of D minor, as in the original). This makes for a more apocalyptic feel to the song, as opposed to the eerie haunting sound of the original.

just changing the key D minor to E minor won't make it more menacing

Personally I prefer this version of "...Eugene", especially the screams; they carry more emotion. This is one of my favourite five instrumentals of all bands.
[no order]
Come In Number 51... ( / Careful With That Axe Eugene) One Of These Days A Saucerful Of Secrets Marooned Hats Of Magic (Acoustic Alchemy)
Shine On

This is one of the best versions of Careful With That Axe, next to the Pompeii version.