While doing some research for yesterday’s post, I came across the proverb “Long in the Tooth.” Like many common phrases, I’d never really thought about its etymology. Long in the tooth refers to how a horse’s teeth change as it ages, becoming longer and more protuberant as shown in the illustrations below.

The images on the left shows the teeth of a 3-year old horse, while the images on the right show the teeth of a 20-year old horse.

The phrase, “Don’t look a gift horse in the mouth” also refers to the practice of judging a horse’s age  — or worth — by the length of its teeth. Recipients of free horses were considered rude if they opened the horse’s mouth to assess its value by determining its age; you should appreciate a gift for the thought and spirit behind it, rather than for its intrinsic value. Of course, in my experience, “free” horses generally turn out to be the most expensive, so maybe it is better to look right away.

Then there’s “Straight from the horse’s mouth.” This may have originated on the race courses of England in the 20th century. When someone has a tip that is so good that it’s better than a tip from a trainer or jockey, it was said to come right from the horse itself. Alternatively, this phrase refers to when people buying a horse would look into its mouth to judge its age.