Quote Originally Posted by it-ogo View Post
here is one exclusion: should be "смотреть зубы коню", I think it is again metonymy: "зубы" is used instead of "рот".
I think not. It is from "Дарёному коню в зубы не смотрят" (You don't look at the teeth of a horse you got as a gift), isn't it? The meaning behind the phrase is that one can estimate the age of the horse examining its teeth. So it is a) no use looking at them if the horse is for free anyway b) kinda rude.
Though the example is not representative for the very basic reason: govenment changes with time. That's where language development is so much like real life.