Slime Mold Fungu
After the slime mold fungus turns brown/black, if you kick it, a brown residue ash-like spray of dust appears. Is this caustic to animals and humans?
Contra Costa County California
The puff of "ashes" you see are millions are spores. Don't worry--they'll just float away. They are not harmful to animals or humans (unless you kick the slime mold and then stick your nose it it, of course.)