(Anesthesia) Pulling Teeth by Cliff Burton. The best bassline I've ever heard.

The other members of Metallica were looking for a replacement to their current bassist, Ron McGovney. According to their liner notes to "Garage, Inc.", they attended a show by Burton's band, Trauma, and heard what they thought was a wah-wah guitar solo. After wondering where the guitarist was (one was not present on stage), they discovered it was Burton playing his famous solo, (Anesthesia) Pulling Teeth, on his bass guitar through a wah-wah.
Burton agreed to join on the sole condition that Metallica would relocate from Los Angeles to the San Francisco Bay Area. He believed the music scene in Los Angeles was "too plastic."
During their tours, Burton deliberately exposed the band to a variety of music styles ranging from The Misfits, Pink Floyd, and Thin Lizzy, to legendary classical pianist Glenn Gould playing Bach.