User blog comment:Babysync/Dust/Aura link speculation/@comment-14817061-20130829022620

Pyrrha stated that Grimm don't have souls. Therefor no Aura. The humans and animals where born from Dust. So the Grimm where born from something else. Perhaps another source of power that isn't Dust? I would like to guess that that power would be Ash, or the black Dust that is said to be illegal.

The story at the begining says that people where born from Dust. The soul itself may be a form of energy that alows humans to use Dust more safely. And why it seams so lethal to the Grimm. I have more but this is just speculation and I don't wanna say anything untill more info is released.