Let's say I'm writing a story from a third person limited perspective. Now, the protagonist/narrator doesn't know what a sushi train is. Would it be wrong to compare something in the story to a sushi train then? Thanks.
If it's third person limited, yes, it would be stepping beyond that boundary. You could, of course, change what your protagonist knows. Remember, you're his creator. The comparison you describe will (and should) carry a significance of some kind, so there has to be a viewpoint through which your reader can filter this detail and integrate it into the story. It's either important because narrator sees it this way or it's important because he doesn't recognize it as such. A secondary character could describe it this way, and your narrator could ask him what the heck a sushi train is, if that moves the story along, builds his character, or plays some other role in the storyline. 'Nother idea: You can also sometimes state what the narrator ignores, or what doesn't occur to him: e.g., John didn't recognize how much this resembled a sushi train (but see how much significance that carries? It's got to be important, or it's probably not a detail worth mentioning at all).
It would be fine. In third person limited, the narrator is not the main character, the narrator is simply a voice that focusses on the main character. The narration, being limited, focusses only on things that concern that main character - their thoughts, their actions, their dialogue, etc - but is not written from their point of view. Therefore, describing something as a sushi train is fine, even if the character doesn't understand the description.
You can think that- that is, the narrator can think that, and can use that description- but John can't. Be sure you're not in his head when you describe it that way, and it'll be fine.
The narrator isn't the author either....you need to make sure you can distinguish between the main character, the narrator and the (implicit) author.
Authors do this all the time. The author will compare an object in a fantasy novel to an oject that exists in our world, but not in the fantasy world. It might be kind of strange, though, if you wrote that he acted like a zombie while writing a fantasy novel in which zombies don't exist. Or if you compared something to Microsoft.
i think it depends more on the style of the novel. if it is a serious 1920's Agatha Christie inspired detective novel then a sushi train is very much inappropriate. but if you take "the witches of chiswick" by someone i cant remember - a book about a man from the future traveling to the more technology advanced past where he finds a time travelling sprout that talks in his head and robots going to fancy dress balls - then the sushi train would be a fine comparison. even if the story was fantasy and not si-fi it is the mood and setting that is important.
