"We do. ...Though I'm not sure any of them have flame sacs, or... anything like that." Whatever the third thing was.

"While most living things are made up primarily of matter, mushi have higher concentrations of pure life force in their bodies. Since they don't have much physical matter to them, those who can't see the life force that they contain can't perceive them at all."

He nods, though it's not particularly enthusiastic. "...Sort of. It's a condition that shows up in people every so often in my world. It's said to a quality of the person's... 'soul', I suppose you could say. Not much is known about it beyond that."