The inside of coke is as sharp as a knife, and the outside of coke melts like cream.

This sentence describes a photographic effect, that is, the focused part and the Jiao Wai part in the photo show different effects. Specifically, the focusing part is described as "as sharp as a knife", which means high definition, rich details and clear lines; The Jiao Wai part is described as "melting like cream", which means it is fuzzy and soft, and the transition is natural. This effect is usually achieved by using a large aperture and a suitable lens.