With lab grown meat we could see the advent of ethical cannibalism.
In Arthur C Clark's 1964 short story "Food of the Gods" a synthetic- meat company came out with a very tasty and great-selling product. Turns out it's cultured human tissue.
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If humans had 4 arms, we'd probably have some pretty wild musical instruments
The main character of the The Hydrogen Sonata by Ian Banks features an alien that had modified themselves with an extra set of arms so that she could play a crazy double necked cello.
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