Of course, he might do it different live, but I've always thought it was him with a Mutron Octave Divider - he gets a very similar sound on occasional notes on live version of Powderfinger etc., and it does sound quite distinct from a quite clean bass sound.
Actually, just listening to the album version now - the bass does seem distinct from the riff, and seems to play the last note before the chords on the beat while the guitar doesn't - those jagged chords seems to be played on two guitars, with the octave effect still applied on one guitar.
I'm sticking to my guns!
Haha, I've just listened to it carefully and I think you're right :). It's funny how things like that get stuck in your head so you actually 'hear' it the other way, until you listen really closely! The actual bass is a bit overdriven, but not that much.
Even funnier, for a couple of years my band (me on bass) covered it and I got exactly that incredible twisted sound with a bass booster going into a fuzz pedal ;). So it's still one of my favourite bass tones... just that the other guy played it :p.
What's funny is that until you two posted, I could have sworn that the mangled bass distortion continues when Neil is playing his octaved solos over the top, thus proving that it's the bass that's so distorted... but no it doesn't :D. And I must have listened to that song literally 500 times.
In my defence I might have been stoned the first time and it tends to stick :).