Visible crew/equipment: When Salma Hayek is tossing the bullet she has just removed from Antonio Bandaras's shoulder, you can see the reflection of Robert Rodriguez holding the film camera on the metal dish.
Continuity mistake: Antonio Banderas throws his guitar case across the roof, then jumps after it and opens it. From the reverse angle the fake guitar inside is still in place, we then switch to it from from the front and it's instantly raised, with the guns visible instead.
Answer: Tito Larriva as Tavo says (in reference to Steve Buscemi) that "This guy smells like shit." The name of the song being played is "Manifold de Amour" by Latin Playboys.