'Kill the pig, cut his throat, his blood.' - what is this line all about ? please explain.

The boys have become enamored by the idea of hunting,
particularly because they begin to feel that it gives them some control over all the
unknowns.  It is a way for them to try to conquer their hunger, their lack of purpose,
and their fear of the beast all in one fell swoop.

The
dance they do to mimic the hunt is their opportunity to draw up the courage that will
allow them to actually kill, something that even Jack shies away from at the
outset.

This line itself may very well invoke that urgent
desire to strike back at their fear, to kill it, to drain it of its blood which gives it
life.