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How the modern pet food industry owes its existence to a US lightning rod salesman, a sailor's biscuit, and the dogs at Liverpool docks. Sarah Stolarz speaks to Dr Katherine Grier, a history professor at the University of Delaware in the US and author of the book Pets in America: A History. (Photo: Beauty the bulldog at the London Bulldog Society Championship Show in 1928. Credit: London Express, Getty Images)