He once told the children about a people made from mud who lived upside down from the surface. They live just like we do, except their floor is our floor, and every step we make is a step for them. Their roof keeps the mud from welling up into their home, like our roof keeps the rain off our heads. 
They have pets and friends and parties and jobs, and in that way they are just like us, except they don’t know about the sun over our heads. They know about a giant glowing molten ball in the centre of their universe, but the stars and the planets for them are merely thicker clumps of stone in the pudding that is their daily existence.
He imagined them throwing out garbage, which for them would be made from bubbles of gas found in the rock and mud. They would bury it into the air above them, which is where all their waste would go, and volcanos, he 
told the kids, is where they dump the gases from cities. Earthquakes are moving day, and tsunamis just a by-product. When lava flows over the top of the ground they dig a bit deeper into their ground, which is our sky, and when there are mudslides the entire village celebrates.
The most puzzling aspect of their world is our intrusion into it. They sense the shafts of our mines, although they see them as caused by a natural force, 
like erosion in a stream, but they view the concrete pylons which support the biggest buildings as stalagmites, but graves are entirely different matter. When a person is buried, they know the ground is opened temporarily and then a vacant space is left in a bubble. Once the grave begins to fill with dirt they get a closer look at a mirror of themselves, and that’s where their philosophy departments begin their work. They have seen buried bodies for millennia, 
but only recently have they noticed the ritual of grave placement, and observed how each buried body takes longer to collapse into dirt than the ones from former years. They know nothing about embalming fluid—although the chemical signature would be recognizable—or hermitically-sealed coffins, mausoleums and tombs. They recognize the general outline of the bodies, and from there they guess at the dimensions of our world even if they can never enter it.
Some scientists have sent probes, and they have drilled into the open air. We experience that as volcanos and sink holes, and some say that even caves are their attempt to mine the air like we mine the rock. They are likely looking for 
gases which they can use in their manufacturing process, just like we seek for minerals. When an area becomes particularly porous, people would move away, claiming that underground streams were undermining the ground beneath their feet. This is the lower world poking its head into ours, and should never be mistaken as a natural phenomenon, like they mistake the mines and foundations of buildings.
The people who most understand those below are the miners. They hear strange sounds in the 
dark, as the pick of their doppelgänger pierces the air just as the above-ground pick thrusts through the rock. For many years blasting was outlawed in mining, and that came from the miners who were worried that they were destroying the world of another with their eagerness for metals. Now their voice is less important when it comes to mining strategies, although when some miners become trapped belowground they talk about shapes in the dark which emerge from the walls and which deliver water and solid limestone nodes. They throw rocks and tap to try for a form of communication, but other than a 
mythical game of soccer deep below ground by miners in Chile trapped for over two months, no one has recorded their statements.
Above ground we go about our daily business, as if we were walking on ants every day, but each of our actions has an effect.
