Over the next few weeks, Vulture is talking to the screenwriters behind 2012's most acclaimed movies about the scenes they found most difficult to crack. What pivotal sequences underwent the biggest transformations on their way from script to screen? Today, Rian Johnson discusses the most pivotal scene in his time travel mind-bender Looper, as told to Kyle Buchanan:

It's the obvious one: the diner scene between Bruce and Joe, which is almost like its own little movie wedged into the middle of a bigger movie. There was just a lot of weight on it for a lot of different reasons. Exposition-wise, it was the scene where we had to address — or choose not to address — all these questions about time travel in the minds of the characters and the audience. I didn't want it to turn into a chalkboard scene, so balancing that with keeping these characters on track for what they actually want was tricky.

This scene did kind of loom as a dragon on the hill, but the way I work is to spend a lot of time on the structure on the film before I sit down to write it. I knew what I wanted these two to butt heads about and I knew where I wanted it to end up, but I didn't know much beyond that, so when I worked my way through the beginning of the script, I was kind of dreading when I would come to it. But then the nice thing about working for so long on the structure is that when it came time to actually write the scene, these people were ready to talk. The bigger problem is figuring out what not to have them say, pruning it back and keeping it tight and economic.

The scene is kind of laid out like a one-act play, in phases: First they sit down and size each other up, then they start messing with each other, and then they both lay out what they want. Basically, for each of the little mini-acts built into that conversation, there was just a lot more of them in the original cut. Bruce originally had this long speech in the beginning where he kind of established his superiority over the younger version of himself by telling this long story about the French language and why he loves it. And originally, there was more exposition about time travel. There's a line in the movie right now where he says, "We're not going to talk about time travel, or we'll be here all day making diagrams with straws," and originally that was a set-up for a gag where one minute later, he actually pulls the straws out and lays them down to start diagramming it out! We did shoot that, but then in the editing room, we realized it was interesting but it wasn't necessary or moving the story forward. We just had to be brutal and slice it out.

It was a real experience for me to work with a dialogue scene of this length and keep it as engaging as any of the action scenes, which was the goal.