Dancing Days sound question

[The Ulnarian]

This post is all about Zeppelin's "Dancing Days".

My question is, "what the hell is going on with the rhythm guitar in this song?". The lead is simple enough, but the rhythm has got to be one of the strangest things I've ever heard. Its strange because it sounds simple and straight-forward on first listen, but as you listen more closely to it there's all kinds of weird stuff going on in there.

I can't figure out what is making the strange rhythm, it sounds like the gutiar is subtely going in and out of tune, although it could be effects, or a synth, or massive harmonization (my guess). Does anyone have any idea what Zeppelin is doing here?

[3fingers]

This is a total guess...I think Page overdubed the guitar with a slide and then JP Jones mixed in Mellotron with a slight phaser on it. ..my 2 cent guess...I would actually like to know as well..