If you're curious about the real ones -
Used as trophies and for ritual, shrunken heads are not quite what you might assume they are. When I was a kid and first saw a TV special that showed them, I was aghast! I had images of some natives along the Amazon boiling my head until it was a raisin.
Here is the recipe for the obscene: The head is severed from the body. A slice is made through the flesh on the back of the head and the skin is peeled from the skull. Seeds are placed under the eyelids and the eyes sewn shut. Pins hold the mouth closed. A wooden ball is used to shape the form. The flesh is boiled, stuffed with herbs, it is dried on hot rocks and sand while being formed. The skin is then rubbed down with ash.
For some time, there was trade in shrunken heads for guns and cash. Since the 1940s, it has been illegal to trade in shrunken heads, which obviously has made genuine ones even more prized. The great majority of ones you find for sale today are animal hides made to look like shrunken heads which is gruesome in its own way.
Are there other ways to shrink a head?
Then, there was the odd case of spontaneous human combustion. This is a very unusual type of case in which a person burns to death, but only part of their body is incinerated to a degree that shows extremely high heat, without burning down the building.