Bycatch from my Snark hunt:
The, well, ambiguity of that “shadow”is known. Also there were some Freudian assumptions regarding what the salt could stand for. But so far I didn’t find any remarks on the impossibility of having a shadow being covered by white salt which isn’t covered by that shadow. To someone who learned physics that is a quite obvious question.
2017-12-17, update: 2020-04-11