What is the connection between Harry Potter and Marie Antoinette? It is a hard, yellowish lump of matter, a concretion formed in the stomachs of camels and ruminants from indigestible vegetable fibre and hair, which is reputed to have magical properties as an antidote to any poison – a bezoar stone.

Harry used one to heal Ron Weasley when he had drunk poison and Marie Antoinette’s spendthrift, playboy brother-in-law – the Comte d’Artois, later King Charles X of France – once owned the large bezoar stone that reposes with its silken cord on a table in the drawing room of Robert Kime’s London flat.

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