It's so simple. Fire off a solid drum beat. Next thing to come to mind: A triplet guitar arpeggio. Fine, throw it on there. Now, bass guitar, do something. Of course, like most Radiohead songs, the bass guitar part gives foundation and transitional movement to what could seem like a bunch of detached guitar dalliances. If Colin Greenwood wasn't in Radiohead, we would never understand what we are hearing. Now it's the vocals' turn to add something. Thom Yorke, probably just one of your typical five-syllable fragments. Hey, I like where we're headed here. Let's just keep piling...
I used this song to teach my boys as tots about how a song is really different instruments playing together. It's surprising how much of an illusion songcraft is, to the point where kids and many full-grown folks perceive music as a single unified sound, and it's a real leap of the mind to isolate the independent sounds that are combining to make it. The song let us point out all the new things coming in, until we would laugh about so many sounds happening at once.
I would wait for the abrupt moment almost everything exits, and it showed us how loud everything had gotten. The backing chimes of this section are exquisite.
While each section of the song uses cyclical-feeling repetition, none of the sections themselves repeat, moving through three different chord structures: A build, a soft interlude, an intense ending.
It's so classically clean, the sculpture of a very experienced hand.