Sacrifice for a qliphotic sphere

in liber azerate page 39 it says: "This should happen after the burning of incense, the delivery of
invocations and prayers to the god or goddess of the Qliphotic sphere, and after a
relevant sacrifice granted to the Dark Gods. "
a sacrifice is not mandatory or is it?
and if it is, I should kill an animal, right?
or is there a human kill?