A Synchestra instrument Question (for anyone)

Hi All,
I have a question about an instrument that can be heard during 'Let it Roll'. It kicks in at 1.23 and it is this bizarre groaning bass-like sound that comes in underneath the guitars. I love it! But I am sure I've heard it before - I believe it is the same sort of thing they used in the intro to 'Orion' on 'Master of Puppets' (Metallica, for those who somehow don't know) - though I suspect it was a bass effect that Cliff used just on his bass guitar. My suspicion is that, in 'Let it Roll', the instrument in question is a double bass that is being stroked by one of those horse-hair wands (sorry, don't know what they're called). But I don't know for sure. Does anyone know what the hell it is? I'd really love to find out - and also if it is the same thing Cliff is using in 'Orion'. Thanks dudes
James.
I have a question about an instrument that can be heard during 'Let it Roll'. It kicks in at 1.23 and it is this bizarre groaning bass-like sound that comes in underneath the guitars. I love it! But I am sure I've heard it before - I believe it is the same sort of thing they used in the intro to 'Orion' on 'Master of Puppets' (Metallica, for those who somehow don't know) - though I suspect it was a bass effect that Cliff used just on his bass guitar. My suspicion is that, in 'Let it Roll', the instrument in question is a double bass that is being stroked by one of those horse-hair wands (sorry, don't know what they're called). But I don't know for sure. Does anyone know what the hell it is? I'd really love to find out - and also if it is the same thing Cliff is using in 'Orion'. Thanks dudes

James.