What an awful story. I would imagine it would be fairly difficult to decapitate someone, I mean, you would have to go thru the spine. Maybe it’s not that hard, but it seems like it would be. At least with a knife.
If you are martial art weapons trained then something like this would be extremely simple to perform.
I may be one of the few on FR with actual experience decapitating a man-sized animal. I used to hunt feral hogs with a knife until I got too old for it.
If you have a good sharp knife, it is not nearly as difficult as you might imagine. You have to find a joint in the spine.
The al queada videos were done with a dull knife and were carried out so as to prolong the agony.