I was thinking about that one recently, the "like shooting fish in a barrel" saying. It's meant to imply something very easy.
What I wonder though is, where did that come from? Who came up with it? What exactly inspired that? My first thought was, this has got to be from the south. I live in the south and that sounds like a saying from around here.
Only in the south would you have a conversation like...
Well, Bill, we got 'em cornered in this barrel.
Yeah but, they're still kickin'.
I know, we've got to think of something...
Oh, I know, GET THE GUNS!
Yes, this situation clearly calls for firearms! You sir are a genius!
After amusing myself with that thought I had another one... wouldn't shooting ANYTHING in a barrel puncture the barrel and drain the water? Why would you ruin a perfectly good barrel? Whoever thought of this saying was not only gun happy, but incredibly wasteful. But that was probably over-thinking it.