With the holidays upon us, suspicious gifts may arrive at your door. You might inspect a horse’s teeth to estimate its age and value. To do this to a horse that is a gift is ungrateful – although, I know something about what it costs to keep a horse, so a sad old plug is a gift you might refuse!

Knowyourphrase says:

John Heywood, who is thought to have lived from the years 1497-1580 C.E., is said to have wrote the saying in a book of his called A dialogue conteinyng the nomber in effect of all the prouerbes in the englishe tongue, 1546:
“Where gifts be given freely—east, west, north or south— No man ought to look a given horse in the mouth.“

Phrase Finder says “As with most proverbs the origin is ancient and unknown,” but also notes that Heywood collected exprssions in common use at the time, and didn’t claim to have coined them.

Heywood obtained the phrase from a Latin text of St. Jerome, The Letter to the Ephesians, circa AD 400, which contains the text ‘Noli equi dentes inspicere donati’ (Never inspect the teeth of a given horse). Where St Jerome got it from we aren’t ever likely to know.

To be over a barrel is to be helpless, at another’s mercy.

The Phrase Finder identifies this as an American expression from the mid-20th century, and refers to a cartoon from the Pennsylvania newspaper The Clearfield Progress in 1938.

Worldwidewords found an earlier citation: “Woodland Daily Democrat of California, dated January 1896: “To use a vulgar expression, a Republican congress gleefully assembled in Washington for the express purpose of getting President Cleveland ‘over a barrel.’ The humiliating predicament…” As often the case, it seems the writer expected his readers to recognise this easily.

The OED suggests that the allusion is to placing a person rescued from drowning over a barrel to clear their lungs of water. This might sound rather unlikely, but there are many references in the literature to show this was once a common practice…

 

There are instances recorded from this period and earlier of a person being placed on or rolled over a barrel as a humiliating punishment. One case was that of a student hazing at a college in Ohio, reported in the Frederick Daily News in Maryland in 1886: ‘Once inside he was at the mercy of his captors, and the treatment he received was cruel. Bound hand and foot, he was rolled over a barrel.’ This is by far the more likely origin, since a person held over a barrel is helpless, whether face down or face up. It fits the meaning of the phrase much better than the resuscitation one does.