Better Know a Phrase: Kappa Phrases

I recently gave a presentation on kappas, mischievous water sprites of Japan, in my language school. I learned a couple interesting phrases on the way:

河童の川流れ: Kappa+possessive+river+flow= the washing away of a kappa. Which means, "even a kappa can drown" or the like. It's very similar to 猿も木から落ちる, or "even monkey's fall from trees." These phrases mean everybody fails, and they are a fun retort to people who notice your failings.

陸へ上がった河童: land+towards+having come up+kappa= A kappa that has come ashore, meaning "someone out of their element". If you change a person's surroundings, even if they are talented, they will be at a loss. Note that 陸 is pronounced おか in this phrase.

Now my favorite:

屁の河童 or 河童の屁: fart+possessive+kappa= a kappa's fart, meaning "a piece of cake to do". I guess farting in the water is an extremely easy thing for a kappa to do. Incidentally as I was giving my presentation, I was searching my mind for the kun'yomi of 屁 (onara) and said "onani", which, well... I won't translate that word, but we must appreciate the patience of the teachers with me.

What can I say, when I speak Japanese, I am a kappa on dry land, and even kappas drown sometimes, though swimming should be a fart in the water for them.
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Bonus: Jeff gave a good answer when I asked for a translation of １０年で　嫁は寝肥り　オレ河童. Why did his translation include Jack Sprat? Check out his comment and see why!