'Skat-monkeys', 'copra-sprites', or 'belly-devils' are considered one of the nastiest and most feared death spells.
The unfortunate victim is given a potion, that includes ingredients not that readily available, such as embryonic cells and milk, either from human or primate, and chopped up thorns and seeds from a certain plant, carefully prepared under ritual.
the 'elemental' that is then gestated within the body causes excrusiating agony once it begins moving, crawling upward with mole like claws.. It usually causes internal injury on its travels, and some of these have been discovered with teeth.
Eventually it lodges itself within the throat, causing a slow aspixiation.