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
[left]: Illustration to Lewis Carroll’s The Hunting of the Snark (1876) by Henry Holiday: The Vanishing (detail from lower left side depicting some weeds which seem to have some fun with each other)
[right]: John Martin: The Bard (ca. 1817, detail from lower left side, retinex filtered and vectorized, then slightly horizontally compressed)
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2018-02-17, updated: 2020-02-01
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2017-12-17, updated 2019-03-10
In a BBC video, video journalist Adam Paylor gives us a good example for why things might be hidden in art: Besides assuming that people who see cryptomorphs in artwork might just be suffering from pareidolia, often one important reason for hiding things in art is neglected by art researchers: Hiding things in images can be fun!
Also from http://severnbeachantiques.com/famous-rare-1980-huntley-and-palmer-rude-garden-party-ginger-nuts-tin you can learn about a good reason for an artist to hide things in art:
I did them out of devilment, purely for a laugh. I’ve always been a bit of a naughty boy but I’ve nothing against Huntley & Palmers. There have been rumours that I got made redundant and did it out of revenge. But that’s not true – I was only ever a freelance. I just felt like adding a bit of smut to the proceedings.
That is what Mick Hill, the creator of the illustration of the Huntley & Palmers garden party ginger nuts tin, said about the hidden surprises in his artwork.