Avis and no - it's not buthead - but it could be...

Sorry, let me get real here...

Avis and Sandy have just finished a conversation in the kitchen, Avis heads upstairs for a shower.

Sandy is still in the kitchen and hears her son Cameron come in the front door and stomp snow off his boots on the hall rug.

Here's a set up of the scene:

SANDY

Get outa here. Go get your shower will you? Dinner will be ready in fifteen minutes.

Avis grabs a radish out of the salad bowl as he departs. Sandy slaps his hand playfully.

SANDY

Look at those hands!

AVIS

(holds up his hands displaying black fingernails)

Hey, I eat lunch with these hands every day. What's wrong with them?

Avis heads off to the shower. off screen the front door opens, sound of boots stomping on the hall rug.

SANDY

That you Cam?

Cameron

(OS)Mumbles incoherently

SANDY

Dinner will be ready in just a few minutes.

Please help me figure out the correct way to write this. Thanks!

anne/JustWriting

looks fine to me, especially for now. You can refine after SF.

Cameron (O.S.)
(Mumbles incoherently) < this would actually be a parenthetical and not written as dialogue.

http://www.simplyscripts.com/WR_format.html

very useful website!!

It is used right after the dialogue. Example:

BOB (O.S.)
Where did you guys go?

"O.S." is used when the character is in the scene but not visible.

"Avis heads off to the shower. O.S.: the front door opens, sound of boots stomping on the hall rug.

SANDY
That you Cam?

O.S: Cameron mumbles incoherently."

OR

"Avis heads off to the shower. O.S.: the front door opens, sound of boots stomping on the hall rug.

SANDY
That you Cam?

CAMERON (O.S.)
(Mumbles incoherently)"

One or the other. I'm not sure which.