Sponge it is, then

Anya: I look like Cinderella because I have a sponge.
Me: [blink, blink] Um... what?
Anya:
A sponge.  You know, on my head.
Me: Do you mean a bun?
Anya:
Um... what?
Me:
The little ball of hair we make on top of your head, that's called a bun.
Anya:
But sponge is so much more pretty.
Me:
Not really.
Anya:
Yes it is.  Please, Mommy, can I call it a sponge?
Me:
You wash dishes with a sponge.  That thing on your head is a bun.
Anya:
A bun is your butt.
Me:
Um... true.
Anya:
So can I call it a sponge?
Me
: I see no reason why not.