I uttered the phrase "happy as a clam" the other day and then wondered what I had just said. Suzanne and I began to wonder how the phrase came to be. After all, when you are a clam, it seems you have two things to look forward to: 1) being stuck in your shell in the bottom of the sea or 2) being eaten by some human or predator otherwise.
To us, neither of those outcomes seemed worthy of the emotion or the phrase. So of course, Google led me to the answer here.
It seems we’re using the short-form of "happy as a clam at high tide".
Interesting. I always assumed it was based on the clam having a very wide grin (if you consider the shell opening it’s “mouth” (which it isn’t) and give wide leeway for the definition of “grin”). I stand corrected.