The Bible says God writes his laws in our hearts, so perhaps what Christ was doing was writing his judgments on the inward places of their hearts(as he wrote on the ground) so that when he stated “Let those without sin cast the first stone”, the accusers would be cut to the quick and would thus drop their stones and slowly slink away!
Just speculation on my part but it was a thought that suddenly had occurred to me so I shared it.
But I accept it might have been doodling. Years ago when I first saw this verse, i thought he might have been just doodling.
I thought of something like that but it would be a lot of writing for something that probbably only lasted a few minutes unless only the essential part of the discussion is in theBible. We can’t know and so far as I am aware none of the saints have received a rlvelation of the matter. We cannot know. It is entirely speculation. I suspect it was primarily so that it was not in the form of a lecture. It is profound and the more so because it wasn’t a lecture. It was a matter of fact suggestion that didn’t stiffen backbones. Whatever it was is in itself irrelevant. The chances that the accusers could read it from standing a few feet away don’t seem good.