Ether 15:30 records the death of Shiz as follows:
And it came to pass that when Coriantumr had leaned upon his sword, that he rested a little, he smote off the head of Shiz.
And it came to pass that after he had smitten off the head of Shiz, that Shiz raised up on his hands and fell; and after that he had struggled for breath, he died.
It seems curious that Joseph Smith would have described Shiz being so animated after being decapitated. If Joseph had written the Book of Mormon, wouldn’t we expect him to simply say that Shiz fell to the ground?
The actions of Shiz after being beheaded are consistent with neural phenomena discovered at the end of the 19th century, which Joseph would not have known about.
Why would Joseph Smith take a chance on saying something that would seem so odd to his readers?