He's talking about tested different opening paragraphs and, how he stumbled into an opener that pulled in more sales than any other he'd written before.
it goes a little like this....
"You've heard the story, I know, of the proud fisherman who was trying to impress a couple of guides with his fishing tale.
'I had a big tarp [a fish] on the line, he was explaing, 'when along came an enormous shark, opened his mouth and just swallwed that tarp whole. Boy, did i have a time landing that shark.'
'Hmm', grunted one of the guides, 'where I come from, we bait with sharks'
Then the letter-writer segues into how no matter how good of a product you say you have... someone is always gonna come along and have a bigger-badder-better one than you do.
I thought it was a great lesson because as copywriters we have to be good at writing stories. It hypnotizes people and moves then further down the page until they're "foaming-at-the-mouth" to buy whatever its you're selling.