Definition - very happy
In case you have a pig, and wish to make it happy, it may be useful to know that, based on our citations, there are many things that will make this animal content. Sometimes the pig is happy in mud, and sometimes it is muck that brings joy to the porcine heart. In the 1860s it was common to see happy as a pig in clover, or happy as a pig in a puddle. The important thing is, should you have a pig, that you figure out what causes this happiness, and then work to procure it.
We are disposed to imagine ourself the luckiest editor extant, and ought to be as happy as a pig in a puddle.
— The Ledger and Texan (San Antonio, TX), 14 Jan. 1860