It never occurred to me that anyone would ever have the slightest difficulty shoting fish in a barrel. Now we're dealing with questions about physics!

I think it only seems problematic if you're picturing *one* fish in a barrel. If you understand the word "fish" as plural, you can see that the barrel is chock full of fish, piled on top of each other -- sitting ducks,in other words, to mix a metaphor.

See -- it's all the fault of that dang English language, failing to diffrentiate between singluar and plural for one particular word, the noun "fish."-- like "deer."