Among the subtle details that I love the most are the expression changes on Ennis' face in the last few scenes that, though almost imperceptible, suggest surging emotions. Somehow he is able to move his face half a millimeter and convey anything from hope to hearbreak. For example, when Lureen mentions Brokeback as being "where bluebirds sing and there's a whiskey spring," he manages to give the slightest hint of a smile as he remembers the source of the phrase, while still looking distraught. Again, when John Twist mentions Jack's plans to ranch with Ennis, he reacts with -- well, it can hardly be called a smile, more like his face slightly brightens, but you can see that he finds knowing that comforting. And of course his face darkens a second later, when he hears about Randall, but again, just slightly -- plus the flared nostrils -- yet we see how devastating that news is.
And the range of expressions he goes through after hearing Alma Jr. say her fiance loves her -- well, that's my OTHER favorite two seconds of the movie.