The English proverb is never look gift horses in the mouth or sometimes expressed as don’t look a gift horse in the mouth. It means accept a gift graciously without assessing its worth or quality. As with all proverbs, they tend to be very old and there is evidence that St Jerome (c.342-420) knew a Latin version of it when writing on the subject of St Paul’s letters. St Jerome wrote, “Noli equi dentes inspicere donati” which means, “Do not inspect gift horses in the teeth.” The earliest form in English is from John Heywood Proverbs (1546): “No man ought to look a gift horse in the mouth.” The way to gauge the age and quality of a horse is to examine its mouth and teeth. The longer the teeth, the older the horse, hence the expression long in the tooth. To be given a horse in the old days was to receive a gift of considerable value. To examine it closely in order to assess its worth and quality was considered bad form.