Principle (n.) undigested are thrown up at once, like food from a weak stomach — mere vomit, foul and unfit to eat.
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A Principle (n.) you never practise rusts like stored armour: one day you take it down and it no longer fits you.
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Principle (n.) unexercised are like old armour stowed away: covered with rust, they no longer fit when needed.
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Principle (n.) are a sheep's fodder: the sheep doesn't show the shepherd how much it ate — it grows wool and gives milk.
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Principle (n.) merely swallowed comes straight back up as a lecture; digested, it shows in how you eat, marry, and put up with an inconsiderate brother.