I'm guessing you are referring to the backwards-sounding quality in the lead. If so, guess what? That's exactly what it is. I'm oversimplifying, but essentially they played the recorded tracks backward and he played the lead in the allotted break (the recorded tracks all sound backwards when you do this). When the tape is flipped and run forward again, you have a backward guitar track over the other "normal" tracks.
Nowadays you can achieve that effect with reverse reverbs and such, but it's not exactly the same, to my ears anyway. It's a great example of how musicians and engineers/producers had to experiment to achieve what were then new sounds. The ingenuity of the day paved the way for us home recorders to do lots of the stuff we do.
Someone with a better grasp of the technical aspect might be able to paint a clearer picture, but you get the general idea.