Yesterday we went to restaurant in the next village which is famous for its clams. You can pick your own clams from a tank and they cook it for you. It got me thinking about the expression “happy as a clam.” Why would a clam be considered happy? A quick google query reveals:

The saying is very definitely American, hardly known elsewhere. The fact is, we’ve lost its second half, which makes everything clear. The full expression is happy as a clam at high tide or happy as a clam at high water. Clam digging has to be done at low tide, when you stand a chance of finding them and extracting them. At high water, clams are comfortably covered in water and so able to feed, comparatively at ease and free of the risk that some hunter will rip them untimely from their sandy berths. I guess that’s a good enough definition of happy. (From World Wide Words)

It seems the expression came into vogue in the mid-nineteenth century. Humorist Eric Kraft’s web-page informs us that the author Louis Kronenberger, the author of Animal, Vegetable, Mineral (1972) (a commonplace book, hence our unfamiliarity with it, I suppose) claims:

“I wish I had made up a word that had entered the language; the most I can claim is to have dredged up a metaphor that was subsequently decapitated. It was a metaphor I found listed somewhere and had never seen in print, whereupon I used it several times in a magazine with a large circulation — ‘happy as a clam at high tide.’ Thereafter I began to see it in print and to hear it in speech in the truncated form ‘happy as a clam.’ Thus what gave it point it had been robbed of: ‘happy as a clam’ is neither good sense nor good nonsense.”