a sparrow egg perched on a duck egg

[IQU3838]

Hi

Does anyone know what the term in the title mean?
I tried to google it, but still don't have any clue.

Here is the context:

"A serene, almost religious smile lit up the woman's face. Her head tilted happily back, like a sparrow egg perched on a duck egg, she smiled into the sun."

Thank you very much for your attention and help.

 

[Raymott]

Hi

Does anyone know what the term in the title mean?
I tried to google it, but still don't have any clue.

Here is the context:

"A serene, almost religious smile lit up the woman's face. Her head tilted happily back, like a sparrow egg perched on a duck egg, she smiled into the sun."

Thank you very much for your attention and help.

It looks like a very strange piece of imagery. I guess it's meant literally - The way her head tilted on her body looked like the way a sparrow egg perched in a duck's egg would look.
What is the source from?

 

[BobK]

:up: It's a very odd image, and not very complimentary. (Thinks: perhaps that's the point :-?... Did she have no waist?)

b

 

[Raymott]

:up: It's a very odd image, and not very complimentary. (Thinks: perhaps that's the point :-?... Did she have no waist?)

b

I was more worried about her neck.

 

[IQU3838]

Thank you very much for your help. It is from a novel. (I guess the author has unusual imagination.)