Many new teachers walk into a buzz saw when they faithfully stay in bounds like for twenty minutes during the CI, and then in one moment of folly, something comes up in the story like when mom says, “You can’t be a gorilla (in bounds) because we don’t have a gorilla suit! (out of bounds)”
The new teacher must know when he is about to go out of bounds and head it off at the pass. He doesn’t have to not say it, he should just say it in English, to get through it. I know, I know it’s all about use of the L2. But if the idea needs to be conveyed to keep the flow of the story going, then just go ahead and say it in English – it just takes a second.
When you say it in English you thereby avoid the quicksand of trying to say it in the target language (they won’t understand it), thereby messing up the flow of the L2, which messes up creation of the “din” in their deeper minds, without which we cannot hope to have acquisition happen.