Attn: People who clean under and behind appliances.
What is wrong with you?
I’m sorry, but I thought that you, like me, understood from a very young age that these dark un-places were not to be trifled with. When you see one of these little cracks in your domestic reality, the correct response is “look away, look away right now, never think about it again unless you have to.” It is most certainly not “squirt a bottle of 409 in there, see what happens.” We inhabit buildings with the understanding that some parts of them won’t cleanly divide into usable space, and that logically some unknowable dark energy will pool there. Why would you stick your hand in that?
Let me lay it out for you in clear terms. If a quarter rolls under the fridge, you are out a quarter. If a sock should tumble over the back of the dryer, it is gone forever. Accept it. Move on. It’s not worth risking the silent treaty we have with that world. What will the creatures who inhabit that space do with one of our coins or goofy foot-pockets? Don’t know. Don’t want to know. Also don’t want to be the guy who poked the wrong shadow creature with a broom handle, and began a psychic war which left us in a broken, threadbare universe.
And while we’re on the subject, stay out of crawl spaces, attics, etc., except when absolutely necessary. Obviously we have to go in there sometimes to fix pipes or run wire, and the other side has to accept that; no utilities means no humans, no humans means no unsettling nega-realm for them to squirm about in. They get to live in the peripheries of our physical space, we get to pump stuff through their presumably-sticky pocket dimension. That’s part of the deal.
But that doesn’t mean you get to just hang out in there and poke around. Go in, do what you need to do, then leave and try not to think about what you saw.
Example: There is a thing in the crawl space under my house — kinda pink, fleshy sorta.* Could be a small animal that died in there. Could be a shed skin of some kind. I have no idea. And I will never know. It’s not mine to mess with. There are rules, and they are important.
*This part is 100% true.