. . . Anyway, it drives home the notion that LaShawn's chatter may constitute desperate (if unconscious) compensation for a rather central problem in her marriage.
There's one scene in which Jack's relative silence always struck me. It's when Ennis asks 2 questions: "You an Lureen, it's normal and all?" [sure.] She don't ever suspect?" [shrug] And then at the dance scene, he hardly says 2 words to Lureen, even as she's confused to the point of prodding Jack as to his lack of attention.
If you think of the film as a musical piece and Jack a soloist, he has most of his melodies in the first half (the dividing line being the post-divorce rejection scene). After that, he's muted (covering his mouth as he weeps in the truck, accepting the hustler's proposition with only a look, and considering Randall's proposition with a shellshocked stare). The only 'noise' from Jack in the 2nd half comes in short, staccato bursts ("Sit down, sonofabitch..." "Go to hell Ennis del Mar", and in the final argument).
^ Ennis' early trauma and defeated nature made him this way from the start. Jack, after the devastating midpoint, becomes like that as well.
