Many go about saying I'm as happy as a clam, or Tom is as happy as a clam, but what are the origins to this phrase and what makes a clam happy?
The earliest in the OED is:
1834 Harvardiana I. 121 That peculiar degree of satisfaction, usually denoted by the phrase ‘as happy as a clam’.
I found a couple of slight antedatings. First from Atkinson's Casket, or Gems of Literature, Wit and Sentiment (Page 571, No. 12, Philadelphia, Decemeber 1833):
On entering, he found the negro in the only dry spot in the house — the chimney corner — as happy as a clam, fiddling most merrily.
Second from a book, The Harpe's Head: A Legend of Kentucky (Page 46, 1833) by James Hall:
He was as happy as a clam. His horses thrived, and his corn yielded famously ; and when his neighbors indignantly repeated their long catalogue of grievances, he quietly responded that King George had never him any harm.
Finally, not an antedating, but an extract of why clams are happy from a six-page discussion of "Clams!" in The Knickerbocker (Volume 11, March 1838):