The said and unsaid. Dialogue and subtext. Symbiotic. Train rails, side by side. The nature of every scene is what is said, and what is really said. Meaning: The essence of the scene, the subtext. What are the actors playing? Have you spoken out every intention and emotion with exposition? Have you left them enough to work with? Let’s look at what to do, and what not to do. First, an example of exposition, the killer of subtext:
INT. DON’S CAR-DAY
DON drives, his pregnant wife DEB, sits in the passenger seat, looking angrily at her husband.
DEB
What’s wrong with you? You’ve been grumpy all week.
DON
Maybe because everything that happened this week has done nothing but frustrate and irritate me.
DEB
Like what?
DON
I’m glad you asked. The first thing is that you’re a week past due date of having our kid. Then my crazy family calls to say that there is a family reunion in Milwaukee. You told my mother that we’d come and now I have to drive 100 miles to Milwaukee instead of relaxing on my day off.
DEB
Are you saying this is my fault? Don’t you remember what you told me? Three years ago to the day! You said you would never go to Milwaukee as long as you lived. You couldn’t face it ever since that episode with Uncle Rocky and the omelet.
DON
I told you about Uncle Rocky and the omelet?
DEB
Yes! But what you never knew was that the same thing happened to me with my Aunt Lucy in the perfume aisle at Marshall’s.
DON
You shopped for perfume at Marshall’s? DEB Yes. I had my own Milwaukee to deal with.
DON
I never knew.
DEB
Now you do.
DON
I need to stop. I’m craving a chili dog.
DEB
Chili dog? That reminds me of that time in Toledo...
Avoid backstory.
Avoid exposition.
Don’t kill subtext.
Leave something for the actor to do. Don’t have your characters speak everything out. When a character speaks about things that happened in the past, it puts the present moment and the present scene on hold. It also puts the audience to sleep. Don’t do it.
Here’s an example of subtext, from Leaving Las Vegas: 
INT. SERA’S KITCHEN. LATER THAT DAY
Yuri is tucking into a hearty breakfast. Sera plays with her food.
YURI
This is such a small apartment, Sera. I cannot stay here. We will find a big apartment. You know how much money I can bring you. I belong in... wealth and luxury.
He suddenly looks up from his food and smiles at her.
YURI
Why did you run away from me in Los Angeles?
Sera says nothing.
YURI
Because you are sly. Mmm? You knew all along that there was more money in Las Vegas. Didn’t you?
Sera nervously plays with her food.
YURI
You have nothing to fear from me. You know why? Because we belong together, Sera. Don’t we?
Sera forces a smile.
SERA
Yes.
A thousand thoughts through her head, and Sera says almost nothing. With an actress like Elizabeth Shue playing her, the camera will pick this up. The character does not reveal her thoughts to her pimp Yuri. She is silent. She plays with her food. When asked, she offers only a quiet “yes” to Yuri’s plans. The said and unsaid.
Here’s another example, same movie: 
INT. SERA’S BEDROOM. LAS VEGAS – DAY
Sera wakes up in bed next to Yuri. She is completely drenched in sweat. A thin shaft o light comes from the crack in the drapes and falls across their bodies. Other than that, the room is in darkness. To get out of bed she would have to climb over him. She lies still. Yuri speaks without opening his eyes...
YURI
You have been lonely?
SERA
I’ve been all right.
YURI
I will keep you safe. We are both older.
He climbs on to her and mounts her. Familiarity.
YURI
You have been lonely?
SERA
I am lonely, Yuri.
He begins thrusting into her.
YURI
Yes... so am I.
Camera move slowly into a tight portrait of Sera.
Sera says it all by not saying it. This is what you want to emulate. One more, from Pleasantville:
He looks at David with pride then suddenly shifts his glance behind him.
MR. JOHNSON
Oh, hello Betty.
BETTY
Hello Bill.
DAVID
Well, look, thanks for coming by. I ... really appreciate it.
Not sure if you remember this scene, but the look between Joan Allen and Jeff Daniels says it all. Which leads us to:
Object Lesson 8: Silence is ok. Actors can play silence.
The Silent Era, decades of movies with minimal or no dialogue. Realize that actors fill in gaps of silence with body language, with eye contact, with physicality. You needn’t say everything on the page. This is where subtext comes into play. Learn this, write subtext, and you will be a better writer.
