They had this massive gong in the studio that Roger hit. When we turned the tape over, the gong sounded great backwards and that sound was going to be at the beginning of the track. That got us wondering what the rest of the track would sound like backwards. Well, it sounded very similar. The riff is palindromic - it sounds the same forwards and backwards. So we decided to run the entire track backwards in the intro and then we seamlessly crossfaded it with the forwards track. I don't think it's even a crossfade - I think it's a butt edit and you can't even tell. I used my fingerboard pickup and bridge pickup out of phase for that tone.