Giant panda Mei Xiang, together with her cub Bao Bao at the National Zoo in 2014. As of Saturday, Bao Bao now has another sibling: Her mother just gave birth to a cub. Chip Somodevilla/Getty Images hide caption

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The National Zoo's carousel is among dozens that Carousel Works has installed around the U.S., each made to fit in with its surroundings. James Clark/NPR hide caption

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No Mere Merry-Go-Round: Ohio Carousel Maker Carves From Scratch

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The New England Aquarium traded 800 mackerel for 12 puffins. OnceAndFutureLaura/Flickr hide caption

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A Dozen Puffins Will Get You 800 Mackerel: Inside The Weird Economy Of Zoos

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In this image from video provided by the Smithsonian National Zoo, Mei Xiang gives birth to a cub two hours after her water broke Friday. A second cub born Saturday was stillborn. AP hide caption

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Dennis Kelly (right), director of the Smithsonian's National Zoo, and Suzan Murray, chief veterinarian, discuss the panda cub's death. Mark Wilson/Getty Images hide caption

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A composite of images from the panda cam, showing Mei Xiang during and after giving birth. National Zoo/Xinhua/Landov hide caption

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