"Andrew, do you know where the phrase, 'no flies on me,' came from?"
"I thought it meant that you aren't too dumb to wash yourself regularly and so you don't have any flies hovering about."
"Now I always had a different image. You say someone is thick because they think slowly, and slow pouring things like porridge or pudding are also thick. Therefore, I thought that you don't have any flies on you because you are too quick for them to settle."
"Gee, I never thought about that."
"Yeah, it means we could be coming up with all sorts of spurious explanations that sound plausible, but weren't the original meaning. It seems to be common wisdom that having 'Buckley's chance' comes from the Melbourne hat shop, though the dictionary doesn't list that origin. Perhaps the hat shop came after the phrase, but fit it so well that people presumed that was its beginnings."