On today's show , we will be talking about an animal that is as impressive and beautiful as it is useful -- the horse . Today's expression is straight from the horse's mouth . “Straight from the horse's mouth ” is about the way we get information and — with this expression — that means directly . When we hear something from the source , we can say we heard it first-hand . It is coming from a primary source . So , if you hear something from the horse's mouth , you hear it from the person who has direct personal knowledge of the information . But don't take my word for it , let's hear it straight from the horse's mouth . ANDREW : I really like to play the piano . The opposite of this expression would be through the grapevine . That is a very indirect way to get information . Now , let's talk about origin . Experts are not sure how this expression started . However , there are two common explanations . One traditional explanation is about buying horses . Before buying a horse , a possible buyer would look into the horse's mouth . This is because you can tell a bit about a horse's health and age from its gums and teeth . Another explanation involves horse racing . At the horse races , people talk about which horses will win and which ones will lose . The most valuable opinions are from the people who know the horses the best – the riders and trainers . Since you can't ask the horse , these people are the next best thing . “Straight from the horse's mouth ” suggests the most knowledgeable source of information . So , this expression can also mean from a reliable source . The information is coming from a trustworthy person . It may even be the definitive source , meaning the best authority . Now , let's hear the expression used in another example : Hey , guess what ? Stella is moving to Toronto ! She's so excited . Are you sure ? She just bought a house a year ago . She told me herself last night over dinner . I just can't believe it . I mean , she also just got a promotion and a raise at her job . It doesn't make sense . Well , whether it makes sense or not , that's what she told me . Maybe you misheard her . I heard it straight from the horse's mouth – Stella's !