a variation of from the horse's mouth, from the original or a trustworthy source. This expression comes from horse racing. Scientists have stated that the most certain evidence of the age of a horse is by examination of its teeth, especially those of the lower jaw. Thus, no matter what an owner may say of the horse's age, by an examination of its lower jaw an experienced person canget his information at first hand, straight from the horse's mouth. —State of ManCongress Approved Gls (14.5.92)