"How's your belly where the pig bit ya?" said the Lonely Lumberjack to me one evening,
"What the hell are you talking about?"
He cackled with laughter. "I don't know. But my grandfather used to ask me that all the time and I thought it was funny. I think it means - how's your belly button."
"Oh. Well my belly button's fine as far as I know. Thanks for asking."
My belly button may have been fine but the rest of me wasn't. I had to know what was behind all of this...
According to R. K. Guest of Erdington, England, his grandfather had been a slaughterer of pigs by means of knife to the throat while the victim lay hog-tied on it's back on a bench - leaving the teeth at the executioner's belly-level, and one had to be careful of bites.
In A Dictionary of Catch Phrases (Routledge, 2003) by Eric Partridge, the phrase is pegged a facetious greeting originating circa 1930. The Aussies, ever the chanters of peculiar sayings, are largely credited with keeping this saying alive. A national survey puts the phrase just into the top 400 Aussieisms alongside If I bought a kangaroo it wouldn't hop [I'm unlucky], Since God's dog was a pup [since a long time] and A few snags short of a barbie [not all there].
Snags means sausages... in case you were wondering.