Duck soup -- the expression not the film

Factual Questions
1

I’ve heard duck soup as an expression for something that’s very easy to do. And I want to know why the phrase was coined. If its directly referencing the Marx Brothers film, that’s fine, I’d just like to know who (in general terms) decided to coin the phrase based off that film. I suspect its older than that, and I’m wondering why the phrase was coined. FWIW, I have a grilled duck carcass that I intend to boil into broth tomorrow, and I don’t expect it will be that much easier than doing the same with a roast chicken carcass or beef roast bones. I guess duck meat is richer than chicken, so it will make stronger broth, is that the reason? Or were ducks easier to catch in farmhouse days than chicken were?

2

Looks like we don’t know.

3

[Rufus T. Firefly]

I can see you right now in the kitchen, bending over a hot stove. But I can’t see the stove

[/RTF}

4

Why a duck?

5

Wabbit Season!

6

In Tim Dirks’ review of the movie, he explains the phrase by quoting Groucho Marx: