This song (sometimes called "Ed's Scary Song") was performed by Ed at the end of the Amateur Night II webcast. It features lyrical snippets from all across the Kid A / Amnesiac era.
A few lines related to this song can be found in the hidden Kid A booklet [click to enlarge]:
There is a section of Fear Stalks the Land with lyrics for this song. It also has a line that would later be reused for 'Thin Thing'.

