The way Zero says 'sewers' tells Jack pretty much all he needs to know, and he smiles wryly. He's hung out in worse places than sewers, himself, on occasion, but it's not somewhere he would generally choose to live either.
What he's most interested in, actually, is the way Zero talks about the vampires from his world - not as 'we' but 'they'.
"You identify as a hunter, rather than a vampire, yourself?" he asks, curious.