What I like about Czernobog is that in this character Gaiman has distilled important stereotypes of Slavic culture. He is avuncular but issues this blood-curdling threat to Shadow, and you feel he would do it.http://en.wikipedia.org/wiki/Chernobog
says Czernobog's mythology is sketchy, but he seems to be an evil god. Frowl says Czernobog is "also known as Crnobog or Chernobog, he is the Slavic god of the dead, the night, and chaos. He is the opposite of Bielebog. "Chernobog" translates literally from Russian as "black god"."
So one wonders why Wednesday would recruit him to his campaign, given these dubious character references. He makes up a rather motley crew when his only motive is to bash in the brains of the hero. It gives the whole pagan enterprise an ambiguous colour to say the least.
I think the discussion of the abattoir is intended to produce repugnance for Czernobog, but also recognition that he did a hidden job that everyone who eats meat benefits from, and an allusion to Upton Sinclair's The Jungle - see http://en.wikipedia.org/wiki/The_Jungle
the great book about the Chicago meatpacking business.The Great Terror - A Reassessment
by Robert Conquest portrays Stalin as a secretive and deceptive tyrant, and made me wonder what is it about the Russian soul that allowed such a monster to come to absolute power for thirty years. Czernobog reminded me of Stalin, with a twinkle in his eye as he plots death.
Norn wiki is http://en.wikipedia.org/wiki/Norns
The frowl summary says
The Norns also appear in The Matrix
as the Fates, creating an apparent link between Shadow and Perseus. Information about the Fates is at http://en.wikipedia.org/wiki/Moirae