What scene do you refer to? At the last time we see them drinking together, the evening before the lake side argument, they share a bottle of whiskey, they pass it back and forth.
I don't know what Jude was observing, but we see them drinking when they're far away from one another quite often -- Jack in the two bar scenes and then at the dance benefit, and Ennis waiting for Jack and then when Cassie picks him up.
(Drinking alone, but then swapping spit -- or in the case of Jack trying to pick up Jimbo, thinking about swapping spit but not succeeding -- with someone else. Ennis and Jack might swap spit with Cassie and Lureen, but they ain't drinking from the same bottle, if you know what I mean.)
(And to Katherine: this is where you can jump in and say that sharing spit via a bottle of Old Rose on the last camping trip is no replacement for getting to see real spit-swapping.
)
(Oh, and to overinterpret symbolism, I guess this means that, when Jack gives Ennis the whiskey bottle after the bear attack, Jack really wants to swap spit. Or maybe kiss Ennis's owie and make it better. Or something like that.)
Edit: and I probably shouldn't even mention Old Man Twist spitting into the cup at the end of the movie, should I?
