For some reason, I've stumbled across a lot of YouTube videos recently that analyze executions. (I had watched a few vids on the Nuremberg trials and I think the YouTube algorithm signed me up for hanging videos, or something crazy like that.)
Anecdotal analysis shows that only about 10% of hangings throughout history have actually snapped the neck and caused instant death. The other 90% resulted in gruesome, lengthy choking deaths, decapitations, broken skulls as the condemned hit their heads on the frames of the trap doors as they fell, and on and on.
Now that lethal injection is being exposed as problematic, too, maybe it's just time to scrap the whole idea instead of trying think of new and creative ways to kill people.
We can go on a battle field and efficiently kill thousands with the press of a button. But, we can't figure out how to efficiently, painlessly kill a single individual in a focused, controlled environment that doesn't require dismemberment of some sort.