I spent a lot of time in grad school studying the fantastic. For my critical thesis, I adopted Tzvetan Todorov's definition from The Fantastic: A Structural Approach to a Literary Genre (1975):
In a world which is indeed our world, the one we know ... there occurs an event which cannot be explained by the laws of this same familiar world.
Is that a DEER driving a town car?
If there is a plausible real-world solution, we have experienced something "uncanny." If something truly supernatural has taken place, we are in the realm of "the marvelous," the world is not as it seems, and all bets are off.
Deer don't drive in our world, so there must be another solution. The brain starts spinning as we try to work it out.
According to Todorov, "The fantastic occupies the duration of this uncertainty."
Marianna Baer's fantastic (double entendre intended) Frost is a great recent example of this. It resolves by leaning towards one end of the uncanny-marvelous spectrum, but I won't spoil it by telling you which.
Fantastic stories often lean one way or another eventually because the fantastic is a balancing act. The reader feels off-balance, and it's the writer's job to keep him there as long as she chooses.
As a reader, I love this not knowing, but as a writer, I want to know everything. Now.
In my current WIP, I keep rushing ahead to one end of the spectrum. It's so much easier to deal with a known quantity, and I'm finding it hard to write something that revels in uncertainty when I so badly want certainty in my plot.
Maybe the fantastic needs to wait for a later draft when I've made some firm decisions about the rules of this world -- it's hard to write the beginning until you know the ending etc., etc. -- or maybe I need to feel off-balance and appreciate the myriad possibilities of this stage.
Have you decided yet about the deer? Was it a man in a deer suit? The next step in evolution? A case of elaphine possession? (That's a word for Linden's grandpa!)
As long as you haven't decided, things are fantastic.
When you decide what you saw was a happy accident, an illusion captured on film, things may get less interesting, but if you're close to the end of the story, a satisfying answer may be exactly what you want . . .
I mean, I will sleep better knowing that deer isn't driving around my neighborhood. Plus, it's super cute.