Here's something I found on Wikipedia (i.e. take with a grain of salt):
"(Anesthesia) Pulling Teeth" is a bass solo by Cliff Burton. An instrumental track, with accompaniment on drums by Ulrich, it features Burton's distinctive "lead bass" style of playing, incorporating heavy distortion, use of the wah-wah pedal, and tapping. This is also the bass solo that Burton was playing when Hetfield and Ulrich first saw him at a gig: “We heard this wild solo going on and thought, 'I don’t see any guitar player up there.' We were both counting the strings and I finally turned to Lars and said 'Dude, that's a bass!' Cliff was up there on stage with his band Trauma with a wah wah pedal and his huge mop of red hair. He didn't care whether people were there. He was looking down at his bass, playing", recounts Hetfield.