In the Doctor Who episode S5E1, The Eleventh Hour, The Doctor and Amy walk past a small pond. The Doctor asks about it, and Amy calls it a duck pond:
What is that?
It's a duck pond.
Why aren't there any ducks?
I dunno, there's never any ducks.
Then how do you know it's a duck pond?
It just is, is it important, the duck pond?
So, what's with the duck pond? Did the ducks get eaten by the cracks, or was there something else going on here?