Off with their heads!  We have all heard that quote from the queen of hearts in Alice in Wonderland.  Maybe you remember the scary story of the headless horseman from childhood?  Beheading is how people were put to death in France via the guillotine and even in current times we have heard of beheadings within terrorist organizations.  What is the fasciation behind "losing our heads".
There seems to be some inherent power placed in our heads, as there should be after all it’s where we speak, hear, taste, feel and smell.  All the senses in one place.  Its what makes us, us.  So is it hard to believe that there are people who believe that their enemies souls leave through their mouths when they die?  Would it be beyond our scope of comprehension to think that if our enemies souls escape their bodies, they might do harm to us in the afterlife? If they could do that, our next thought would be how do we do keep the souls in the head.  This is the belief of the Shuar. The most popular of the headshrinkers.  This is a brief history of head shrinking, and the story of Enno Lolling,   a NaziGerman doctor who allowed  the abuse of the dead bodies of human beings.  Not only that but he experimented with head shrinking, himself.

https://en.m.wikipedia.org/wiki/Enno_Lolling
https://www.smithsonianmag.com/smart-news/how-does-one-actually-shrink-a-head-5994665
https://www.allatsea.net/the-head-keepers-of-modern-day-indonesia/
http://holocaustcontroversies.blogspot.com/2017/11/nazi-shrunken-heads-human-skin.html?m=1