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My (Italia-American) mom sang it to us as follows, anyone heard this version?:

Twenty white horses on a red hill

now they dance, now they prance, now they stand still.

All these white horses to me belong.

Up again, down again till they're big and strong.

1) How do teeth "stamp" or "Stomp"?
2) Why would a person suspect horses to be teeth? or a red hill to be gums?
3) How would a person reading The Hobbit for the first time, know that hobbits have 30 teeth by the time this riddle is mentioned in the book, when its never been mentioned by this time?
4) Why does the author expect the reader to already know the answer, without the apparent key information of the number of hobbit teeth, or knowledge of what stamping is in regards to teeth?

Students: We have free audio pronunciation exercises.

I guess they're mating like horses, too, by rubbing eachother