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What Is a Gift Horse, and Why Shouldn’t You Look Inside Its Mouth?

The origins of this odd equine idiom come straight from the horse’s mouth.

Nice chompers.
Nice chompers. | Guido Mieth/Stone/Getty Images

Like many old proverbs, “Don’t look a gift horse in the mouth” used to have a very literal meaning before the passage of time turned it into a figure of speech. Not looking a gift horse in the mouth means being thankful for a gift, even if you secretly wished for something better—and it originated long before the invention of cars, when horses were widely used for work and transportation.

The first appearance of this proverb is often traced back to the London-born writer John Heywood’s Middle English text A Dialogue: Of the Effectual Proverbs in the English Tongue, published in 1546, in which the author argues that “No man ought to looke a geuen horse in the mouth.” 

However, the proverb appears to be much older, with etymologists pointing to Saint Jerome of Stridon, an early Catholic priest who—in his commentary on the Epistle to the Ephesians in the New Testament, dated to 400 CE—wrote, “Noli equi dentes inspicere donati,” which translates to “Never inspect the teeth of a given horse.”

The saying seems to have taken on its contemporary phrasing sometime during the 17th century, The poet Samuel Butler incorporated the line “He ne’er consider’d it, as loath / To look a gift-horse in the mouth,” in his popular 1663 poem Hubridas, setting a standard subsequent writers would follow.

But why a horse? And, more specifically, why its mouth? As any modern-day equestrian could tell you, a horse’s teeth betray its age. “Horses have two sets of teeth, baby teeth and adult teeth,” according to a post by the New Jersey Agricultural Experiment Station. The older a horse gets, the more its adult teeth elongate and project outward. (From here we get another equine idiom, “Long in the tooth.”) 

“When people needed horses every day, a horse’s value was based on his age. So if you were going to buy a horse, you would want to know its age before offering a price,” the post continues. However, if someone offered you a horse for free, it was considered rude to look into its mouth and inspect its age—just as it is considered gauche today when you look up your Christmas gift’s price tag on Amazon. 

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