Well most of them fail to recognise that whilst they see that there's an underground system they sit on the surface, see where I pop up and then claim to know how I got there and understand the journies by tracking the distance as the crow flies.
What they don't get is that there's a whole network beneath the surface. A labarinth of tunnels, dead ends and exits. Whilst they may walk in a two dimensional fashion, claiming that a hill is their third dimension, I've gone up and down beneath their path, going through the foundations of their obstacles and pathways. Quite often when I express I'm talking about the things which lie underneath what they see and they just don't get it.
That and people often assume that because I don't conform to standard distribution curves that I'm doing something "funny" and view me with suspicion.