Well, it's not a joke - actually, this isn't a joke thread - it's a silliness thread, although jokes are posted.
OK, so I'll explain it to you like your an Obama voter - take a close look at the duck - doesn't it appear to be happy and smiling, possibly showing anticipation of a treat? That doesn't happen often, but perhaps you don't feed ducks treats, perhaps you live in the hood and there are no ducks around?
Anyway, silliness is in the eye of the beholder.
I've never been around ducks, but chickens sometimes had that look on their faces. I guess that's why I didn't get it.
Thanks!