In 1 Nephi 17:41 it says:
And he did straiten them in the wilderness with his rod; for they hardened their hearts, even as ye have; and the Lord straitened them because of their iniquity. He sent fiery flying serpents among them; and after they were bitten he prepared a way that they might be healed; and the labor which they had to perform was to look; and because of the simpleness of the way, or the easiness of it, there were many who perished.
This is curious because the King James Version of the Bible does not speak of “flying” fiery serpents related to this story Nephi was referencing. So why did Joseph Smith include that extra word?
The underlying Hebrew word used to describe the fiery serpents in Deuteronomy 8:15 (seraphim) means a winged creature so Joseph Smith was entirely appropriate to add the word “flying”.
How would Joseph have known about the underlying Hebrew in the King James Version of the Bible?