shape, figure, and body

[yuriya]

Hi, everyone. I am reading a book about common English mistakes made by foreigners and got curious about this:

A: Why don't you have some more cake?
B: I want to have a nice shape. (wrong)
I want to have a nice figure. (correct)

The gist of the explanation given is that you use "shape" as in "stay(keep) in shape" and "figure" as in "have a nice (good) figure."

Unfortunately, I looked up "shape" in my dictionary and found this:
She has a beautiful shape, with small waist and curvy hips.

If the explanation given in the book is correct, shouldn't it be like this?:
She has a beautiful figure (or body), with small waist and curvy hips.

Thanks in advance!
__________________
Feel free to correct my sentences. I welcome them, not resent them!

[birdeen's call]

Hi,

"I want to have a nice shape" is not exactly a wrong sentence. It depends on what you call wrong. It may be unusual but it's meaningful and grammatically correct. It's just that people don't say it that way.

Your dictionary example could surely be reworded by replacing "shape" with "figure" or "body" but someone wanted to use "shape" and they had a perfect right to do so.

That's my opinion, not facts.