I was watching a movie, and the subtitle said, "Yeah, that's it, just lie there." I know that movie subtitles can always be incredibly inaccurate, but I was wondering if it's correct to add a comma before "just lie there." Would that be a comma splice, or is it correct the way it is?
"Yeah, that's it, just lie there."
The actual purpose of the comma is to indicate where you would insert pauses if the sentence was spoken. Since this sounds natural as spoken dialogue, it's fine.
As a counter example, consider this:
Yeah, that's, it just lie there.
With the comma in a different place, you now have "it" paired with "lie", which totally changes the meaning (and is ungrammatical), and leaves a hanging "that's" which isn't paired with anything. However, you never know -- this could be a meaningful line of dialogue in some strange context.