Well, for one. I've seen evidence that they had to do very normal things to hide the blueprints of their building. I saw a fragment of them tucked into a filing cabinet, in a place where someone might find something old like that. It was torn out, like they were hasty to get rid of it...

And yet, it was still there, plain as day wen I looked and found it, in a place we shouldn't have been able to find normally. They have covered their tracks well, and they're very powerful... but they aren't perfect. Despite all they try to seem, I think they're still very human.