Quote Originally Posted by David75
In fact it seems Shinigamis can control the interraction their body and matter from our plan of existence.
I would guess this is a concious action, which could let us think that the sand, being inert, can't interact with matter from our plan of existence.
Well, I didn't really mean to start a real discussion about such an irrelevant subject, but like I said in my post, if it was unable to interact with matter of this world, then it wouldn't have piled on the floor, but would have fallen into the abyss far below.

If it turned into just normal sand and dust like Psyke suggested... Well, that would actually mean building a sensor to detect shinigami would be far more easier, because no fundamental differences would be between the shinigami world matter and our world matter, and the only factor would be to break the trick rendering them invisible. Shouldn't be too hard, really, seeing how they would be made of the same stuff, but only had some cloak. Kind of like the stealth fighter radar invisibility can be countered with more sophisticated radars or other sensors.