Waiter, waiter, what soup is this?
It's bean soup, sir.
I don't care what it was. I want to know what it is now.
This joke is a double pun. It is possible only because the waiter uses contraction (it's).
it's = it is OR it has
it is bean soup
it has been soup
bean (noun): an edible seed
been (verb): past participle of "to be"