Not that I've ever had a conversation with a shark, but I suspect that rather than any nutty aftertaste, it's primarily the bone/meat ratio that turns them off. Most fish have soft bones and lots of flesh. I think that even seals are fairly fatty. But humans are just lots of bones with a bit of flesh and fat (though this may not be true of all Americans nowadays). Just think of it. Lions usually chew the flesh off the bones, but sharks just munch things down. Just imagine trying to chew up a leg, tibia and all. I don't think it would be all that appetizing.

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As above, so below