The trailer for No Country For Old Men is a wonderful lesson in simmering intensity (full disclosure: it was produced by the trailer house that I worked at as an assistant editor). Just like the film, the trailer's score is pretty sparse, and is somewhat atypical in that each section unto itself doesn't feature music that is on a constant rise, and yet the progression from section to section clearly shows that overall the trailer builds in intensity.
The film itself has only the barest of what you might consider a film score, but in both the trailer and film, the soundscape beautifully serves to enhance the menace of Javier Bardem's assassin character. Just like his character, the trailer is a mix of slow burn moments punctuated with bursts of intensity. The direction of this trailer is to tell us why Bardem is after Josh Brolin, and spend the rest of it making him out to be a very bad dude.
The trailer starts with Bardem's coin toss. The trailer liberally uses cutaways to distill the 4.5 minute scene down to focus on the coin toss. The cutaways not only save time, but give the audience the impression that Bardem is dangerous via the juxtaposition of the bodies in the desert. The scene in the trailer ends with Bardem saying "friendo" which is a re-ordering of the scene's dialogue, but is a very short, snappy and threatening way to get out of the scene.
After this cold open we get some light guitar music under shots of Josh Brolin's character stumbling upon the bodies. The title card: "In the open country you can find anything" serves as an ellipsis to transition to Kelly MacDonald asking Brolin about the satchel he picked up. Once he mentions that it's full of money, we get some simple see/say editing of him finding the money, Woody Harrelson talking about his money, and an ending with MacDonald saying she has a bad feeling.
There's another series of title card ellipses saying: "But every fortune... leaves a trail" to introduce the police starting their investigation; the guitar music ends on a deep hit which transitions into a subtle drone. The section ends with Tommy Lee Jones saying: "If it ain't, it'll do until the mess gets here" which perfectly segues into a horror sting sound effect with Bardem saying he's looking for Brolin's character.
Bardem talking to the woman about leaving a message for Brolin is punctuated with shots of him breaking into the trailer. In a typical trailer, these punctuation moments typically end as soon as their sound effects finish, but here there's an ominous breath as the door opens. Bardem's "yes" is repeated for the sake of the trailer before the car blows up, which leads us into the next act of the trailer with a new music cue..
Usually trailer music works best when it's building, but here the music doesn't really build; instead it always returns to its original intensity, which emphasizes the bursts of action when they happen. In fact, in this section Bardem's exhale after killing the man directly parallels what the trailer is doing in terms of giving the audience an intense moment, and then letting them have a breath as it cues up the next one.
There's a brief series of shots to set up the climax of the trailer. Tommy Lee Jones' line ostensibly says to the audience: "Okay, here it comes!" We get another breath after another briefly intense montage. The old man's "can't stop what's coming" is another classic trailer line of "Now see what's coming!" which leads us to the final climax.
The music here is almost steam train-like as it backs up more lines of dialogue that all serve to build up the danger of Bardem's character even more until we get another breath as Bardem's air tank hits the ground. After this is what sounds like some sort of air pressure rise sound that leads to the thunderstorm and final montage that bookends the trailer with Bardem's coin toss that perfectly leaves the audience hanging. What's going to happen???
This is a very spoilery looking ending, but the visual itself isn't so striking that the audience is likely to remember it long after seeing the trailer. And this ending doesn't feel very spoiler since the ultimate question of the trailer is: "Is Josh Brolin going to make it out alive?" not "Is Kelly MacDonald going to make it out alive?" though even if it were, the trailer still doesn't answer that question.
This trailer is just a fantastic example of a trailer that understood its source material, and managed to evoke the feeling of it even in its shorter and more bombastic form. The creative decisions around the music in the trailer reflect the tone and pace of the film. I don't think there are explicit editing lessons that can be transferred from this trailer to other ones, but it's always important to match the tone and feel of the original (provided that tone is something interesting).