Warning: I am no scientist, and this is all headcanon anyways. Apologies Mr. Weir, I am taking your established canon and spinning new lore with it
So much of life in the deepest parts of Earth's oceans are bioluminecent, it makes me wonder if life on Erid could be similar. Perhaps not in major metropolitan areas, which could explain why Grace's biosphere is surrounded by darkness in the books, but those sorts of enviroments are generally low on Interesting Fauna anyways.
And what if, having a history of being a predator of creatures that created their own light, Eridians could sort of "hear" when something is giving off light.
I have visual snow syndrome, and it gets signifigantly worse when looking at anything that gives off light. So I'm imagining little rock spiders observing a static-like "texture" over the actual texture of bright things within earshot. It probably wouldn't be as intrusive as it is for something that can actually see light, such as myself, but still enough of an effect to notice and draw conclusions off of.
