Lately I've encountered two novels which annoyed me because they treated burro and mule as synonyms, which they are not. The most recent was Abandon, by Blake Crouch; the title of the other one does not leap to mind.
 
    Mules and burros are related, but they're not the same animals. Start with the familiar horse, Equus caballus. An uncut male is a stallion and a female is a mare.
 
    Then there's the burro, Equus asinus, also known as an ass or donkey. Males are jacks and females are jennies.
 
    Donkeys and horses can interbreed and produce offspring which are almost always sterile. Most commonly, a jack breeds with a mare to produce a mule, which has big donkey-like ears.
 
    When a stallion and jenny breed, the result is a hinny; they're odd-looking beasts and the only time I've ever seen one was in a comedy act at the county fair rodeo.
 
    I asked a mule-breeder friend about the differences between hinnies and mules: "A mule generally gets the best of both parents -- a donkey's smart head on a horse's strong body. A hinny usually turns out the other way around, which is why hardly anybody breeds them."
 
    The burro has bloodlines that breeders track. As for the sterile mule, the old saying is that he has neither pride of ancestry nor hope of posterity (though racing mules have been cloned in recent years).
 
    The big ears on the mule inspired the name of our Western mule deer; the jack rabbit, with the long ears, gets its name from jackass-rabbit.
 
    But even though they both have equine features with some impressive ears, the mule and the burro (or ass or donkey) are not the same, and I wish people would quit confusing these animals that continue to do a lot of the world's hard work.