What does a mortal have to do to be able to see god machine infrastructure? I'm trying to remember if there's a roll.  I believe seeing it carries the risk of becoming a stigmatic? is there a roll for that? or is this all more or less a function of the story? I decide that they can see the gears, and whether or not they should become Stigmatics.

I plan on having my players (not demons) stumble upon a "blood treatment plant" — it's like a water treatment plant but with blood.