Experimental Archaeology 4: but what is Julie doing?

I can't figure out what Julie Fissenden is doing in this photo: it looks as though a fair-sized log has been upended and then had a fire built around its base.  It seems to have been burned about half way through without falling over.  And what's the whiteish thing that Julie is adding to the fire? There are a couple of other similar items on the right side of the fire.  Magnified they look like bones or scrolls.  General mystification.

"Come come, Crickley Man, it is all very clear. Julie F is stoking the fires (by throwing on a billet) around a make-believe house post, to see whether the burning of a house would cause posts to char below the level of the ground surface. Postholes, you see, regularly have charcoal in their infill. The answer, however, is probably not. The charcoal must derive from other sources, rather than the burning of the post itself. Clear?  Phil."

Clear!