We are veering into morbid seas....
Just my 5 cents:
The quest for instantaneous and complete decapitation is centuries old.
Because even highly trained men could not always do the job right with an ax or a sword, did Mr. Guilloten invent his machine. It was advertised precisely from the humanistic point of view: no pain, instant death etc. Mr. Guilloten was himself beheaded by his invention later on, but his personal impression is yet to be published....