Quote Originally Posted by Shady_arc View Post
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.
That's what I mean. Examine teeth = смотреть зубы (like a dentist). But to examine teeth one should look into a mouth, смотреть в рот. Here we have a metonymy when we spread the meaning of рот to зубы to express both ideas simultaneously.