Additional Dialogue Replacement
That is what happens in post production, often months after the filming of a series or a movie. The editor, or even story producer might need to fill in some missing components to the narrative. A reference that was filmed may have been a little vague, perhaps.
Sometimes its about the need to replace audio that was distorted, or inarticulate. The lapel mic may have rubbed on a jacket and created a mini storm inside that segment of dialogue - or the wind was up and the 'dead mouse' on boom mic wasn't enough of a shield.
It gets tricky for the actor, especially after a long time away from the emotion of a scene. (In the sound booth, she/he would need to re-create the emotion, or the physical presence of that voice in the scene. Which may even mean using breath and all the physicality of whatever was happening IN the action of the scene, in order to get there.)
I really enjoyed working with the UK actress in a scene from the new ENDOR series of 'Deep State'. (There are NDA restrictions on mentioning who and what was filmed, but the scene was directed in a way, by Joss Agnew, that gave us a stability on set, with so much room to explore. It was shot like a documentary, buy a DOP with that kind of 'fly-on-wall' spontaneity.)
A few months into post, and here were are, in BoKaap at the studio of choice for many of the international productions that shoot here in Cape Town: The Workroom. With direction from a remote London audio production suite. Clear as a bell, and instant.