Screenwriting : Mouthing Words (format) by Kimmie Easley

The most proper way is to write it as an action line, and not as a dialogue line, because of production reasons, and also because we don't hear it. The character is not saying it, they are mouthing it, and it would go like this:

Kimmie looks at Bill, and mouths the word "thanks."

What's the purpose of this scene? is it a word or short phrase that we should understand or is it more like a private conversation that's hidden from the viewer at that point in time?

If it's the latter then you might use something like:

Kimmie leans into Bob's ear and delivers unheard orders.

If it's the former then it could be as simple as:

Kimmie mouths - Oh shit.

or

KIMMIE (MOT)

Oh shit!

There are many ways to get this across depending on your intention and how you want it portrayed.

It appears to me since it's not actual dialogue it's in the action line. In The Screenwiter's Bible, 5th Ed. p. 222, David Trottier writes, "EXT./INT. VAN - DAY The van rumbles along. Inside, two twenty-something parents, RALPH and SALLY shout at each other, although they cannot be heard." In a script I wrote, I put it this way in an action line, "Matt hams it up behind her, mouthing 'Ok control freak'." Hope this is helpful.

Looking at the screenplay for the film MUD as an example... Ellis is outside the window watching his parents argue inside in the kitchen. His mother suddenly glances over at the window and outside as written in the script: Ellis quickly ducks and mouths the word "shit." This example is on page 2. ;) Hope that helps, Kimmie!

There! From Beth! Read scripts. Everything you need to know is on the page. Read and copy/steal. .

We need to know in what context. E.g. is the character mute and actually having a conversation mouthing the words? (In which case are they may be gesturing the meaning at the same time.) Is the scene seen through a window or from a long range as a POV therefore MOS? Is the person speaking mouthing something to be secretive? Do you want the audience to know what is being said or not? Is it one word or an entire conversation. All these examples could be handled in different ways (as some have already purposed.)

The action is the character holding a patient, like a hug, while mouthing the words 'Just go with it' to a co-worker. Thanks to all and Beth Fox Heisinger , that's a huge help. Thank you!

I actually did A LOT of research on this for a scene I was writing. I believe Pierre is right - either way is acceptable.

I've seen it being done in action lines, I've seen it in parentheticals. Just be consistent.

Thanks for the feedback!

That was a typo and was meant to be MOS.

Laura, a veteran producer of over 40 films told me that same story! I believe the German director was Otto Preminger! And, he said the same thing to me, he pronounced it as "Mit-out sound!" I still tell people on sets that. Also, I'm a genius at shooting MOS! ;) GOD BLESS and STAY FRESH!