Jonah and the big fish story show the level savvy that existed back 1000+ years ago. How many people would know how impossible such a thing would be. People were very ignorant then by the standards of our modern world views, so a fish story like Jonah's was excepted with out much questioning.
Even today many take a childlike view of the story and are totally oblivious to its to its impossibilities because it is hard to remove ingrained ideas we got through heavy indoctrination. But I don't think such ignorance will last now that we are in the information age.