It's always an awkward moment in any role-playing game when the game master has to represent two, or worse more, non-player characters talking to each other. The exercise resembles nothing so much as young Danny's conversations with his own wagging finger in "The Shining." Using funny voices, the GM ekes out an extended scene while the players sit and watch.
But this is as destructive of the social nature of RPG as any paragraphs-long set-piece room description or boxed text would be. The point of the game is to construct a shared reality through interaction. Awareness that you, the GM or player, are entering into a monologue-as -dialogue should be a sharp signal to shift gears.
To what, exactly?
While some advise to skip such scenes entirely, I don't think it's possible or desirable. Instead, what I do now when I feel a sock-puppet play scene coming on is to paraphrase. That is, switch from this:
COURT WIZARD (bad Peter Lorre impression): Eeeuhh, my lady, what these adventurers propose is verrry reckless.
QUEEN (bad Renee Zellweger as Bridget Jones impression): But the bones of my forefathers are endangered if the rumors are true!
COURT WIZARD: They were placed there to watch over an ancient evil! Who knows what these bumbling louts will awaken?
YOU: The Queen supports your mission to rescue the bones in the tomb, but the wizard is agitated and warns her that you may disturb an ancient evil.
This leaves it open for the players to intervene and address either party, at which point a player-GM conversation can take place in character again.
Come to think of it, the goal of maximum interaction also suggests a light touch when describing scenes, but that'a topic for next time ...
5 minutes ago