Of Jacks and Jennets: Facts About Donkeys - The New York Times
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Mule's foal fools genetics with “impossible” birth – The Denver Post
Befuddling Birth: The Case of the Mule's Foal : NPR
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Are Mules, Burros and Jackasses All Donkeys? | HowStuffWorks
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Hinny - Wikipedia
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Mule - Wikipedia
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