Haha sack is more of an inside joke. At the time when we had created that chapter we had a Facebook poke war going on.... So we decided to look up the word poke in different languages. Sack is how you say poke in German. Basically they're just yelling poke at each other. XD
I just read the first chapter, and I think this story has potential. I like the humor although at times it seems to overpower the zombie apocolypse mood and I don't really understand "sack."