Screenplay Description: Only Sight and Sound

By John Glenn

Show, don’t tell. That’s the byword for movies. And screenplays. When we experience a movie, the only kind of information we absorb is what we see and what we hear. That’s it. Everything springs from those two sensations—sight and sound. Since your screenplay is supposed to replicate the experience of a movie, it follows that your script should only convey what is seen and heard.
Look at this passage from The Shawshank Redemption:
The BUZZER SOUNDS, the cells SLAM OPEN. Cons step from their cells. Andy catches Red's eye, nods his thanks. As the men shuffle down to breakfast, Red glances into Andy's cell –
– and sees Rita in her new place of honor on Andy's wall. Sunlight casts a harsh barred shadow across her lovely face.

Read over those lines carefully and you’ll see that there is nothing there that is not visual or aural. Nothing. We get a very strong sense of the prison—the mood, the routine, the relationship between Andy and Red, the magic of the Rita Hayworth poster. But we get it all from what is seen and heard. 
What about the other senses? Smell, taste, touch? You don’t include those in a screenplay because you can’t see smell. Or taste. Or touch. You can’t hear them either. However, you can see and hear a character’s reaction to these stimuli. So if you want to convey these senses, you could do it like so: 
Bacon sizzles in a frying pan. Tim leans toward the pan and inhales, eagerly. He reaches in to seize a piece of bacon. Shoots back his hand.
He sticks his finger in his mouth to ease the burning.
Then he picks up a fork, stabs a slab of bacon, lifts it up, takes a bite. He chews, closing his eyes with pleasure.

There, we managed to convey smell, touch, and taste through sight and sound, and without too much trouble at that.  
What about thought? When you’re writing prose, you’re free to include the thoughts of the characters. Indeed, that’s one of the charms of reading fiction, the ability to dive into the minds of the characters and see what’s going on there. With screenwriting, sorry. Thoughts don’t work. You can’t see thoughts, can’t hear them. So you can’t do something like this:
Bacon sizzles in a frying pan.
Tim reacts in horror, remembering how his father was tragically killed in a horrible fire at a bacon factory.

That’s a memory, a thought. It won’t show up on film so you shouldn’t include it in a screenplay.  If that tragic fire is important information, you’ll have to find another way to convey it. You could show Tim’s horrified reaction then dissolve into a flashback of the fire at the bacon factory, but, as you’ll learn later in this book, flashbacks aren’t usually a good idea. So you’ll probably have to do something like this:
Bacon sizzles in a frying pan.
Tim rushes to the stove and turns off the flame.
Mom, how could you? After what
happened to Dad?
And then the conversation turns to that fateful day at the bacon factory. Okay, it’s still not great screenwriting but at least it’s not violating the see-hear rule.
Let’s look at some better examples of how screenwriters manage to convey thoughts while staying within screenplay boundaries. This bit from Die Hard comes right after McClane narrowly escapes a barrage of machine gun fire:
McClane remains motionless in the air duct. Three quarter-size holes inches from his face. Sweat covers his face, drips silently onto the aluminum.

It’s real clear what McClane is thinking here: “Holy shit!  That was close!” Or maybe he’s thinking, “Holy shit! A bullet almost went through my brain!” Regardless, whatever he’s thinking most likely starts with “Holy shit!” and has something to do with not being dead. We know what McClane is thinking because we see three quarter-size holes inches from his face and we see that sweat covers his face.

Truth is, you can cheat a little with thoughts. Just a little, though. Look at this bit from Sideways, right after Miles bungles a romantic moment: 

After a few seconds, Maya breaks away and steps past him, heading back into the living room. Miles realizes he’s blown it and silently berates himself.

Here the script is actually giving us a thought: Miles realizes he’s blown it.  But the thought isn’t coming out of nowhere. It’s directly related to physical action—Maya breaking away and Miles silently berating himself. If the actor plays the moment right, we’ll be able to sense exactly what he is thinking. 
In this bit from Sideways, the script cheats even more:
She takes a seat opposite Miles on the couch. They look at each other without speaking. Just what is the vibe here?
Here the script is actually quoting Miles’s thought: Just what is the vibe here? And the thought isn’t as directly tied to physical action as in the previous bit. The two characters are just sitting there in silence. Still, the thought is closely related to what is happening in the moment and it’s possible for an actor to convey it through the acting. Now and then, you can get away with something like this—as long as it’s possible to convey the thought on screen. If Miles were remembering the fire at the bacon factory, that wouldn’t work.
Finally, three minor points in the see/hear department:
Don’t use the words we see or we hear to indicate what is being seen or heard, unless it is unavoidable. For example, it’s better to write Darkness than We see darkness. It’s more direct.
Don't describe the style or placement of the opening credits in your script. Credits are figured out in the production stage, and sometimes movies don’t even have opening credits. Sure, credits are cool, but forget about ‘em.
Don’t describe the musical soundtrack at all. At the production stage, a composer will figure out how to capture the mood of the moment in music. It’s okay, though, to refer to source music, that being music that the characters hear in a scene. For example, when a character plays a recording or attends an opera. But with source music, refrain from citing a specific contemporary song—rights can be a problem and do you know how expensive a tune like “Satisfaction” would be? Instead put it this way: He plays something with an irresistible old-time rock beat.
This passage appears as part of Chapter 4 in Gotham Writers’ Workshop’s Writing Movies: The Practical Guide to Creating Stellar Screenplay.