Voodo qestion necromancy

Ok so in a book i read the necromancer he say bokor voodo guy, it follow giving instructions. To follow the body. Then he switch to offerings to the demon. I knw tey use loas, spirts, veves etc. But it say demons, offering, wen in the begining for necromancy ritual. No say tat.? Why it switch,? Bcse its a mix of magik,? Or the author was bad translating,? Thanks