Christopher Walken & Dennis Hopper are gods among men.
The music is The Flower Duet from Lakmé by Léo Delibes. http://youtu.be/8Qx2lMaMsl8
Tarantino himself has named “The Sicilian scene” as one of his proudest moments. “I had heard that whole speech about the Sicilians a long time ago, from a black guy living in my house. One day I was talking with a friend who was Sicilian and I just started telling that speech. And I thought: ‘Wow, that is a great scene, I gotta remember that’.” (From the unrated director’s cut DVD commentary.) http://youtu.be/fXxhbrsuDSQ?t=2s