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Reading scripture in front of a donkey. The country of origin of this proverb is Afghanistan (as far as I know) but we also have exactly the same idiom, identical in meaning, in our native language - the gospel was being read in front of (above the head of) a wolf but he was howling - let me go, the sheep are fleeing!
We use this expression when we want to emphasize that talking to a person (getting through his/her thick skull) is a futile endeavor; it's useless. I had been talking about the dangers of tobacco to him for an hour or so, when he took out a pack of cigarettes and started smoking.
I would like to know whether there is an equivalent expression in English, germane to the above-mentioned one?