Describing facial expression


**Edit:** The link provided by @broken headphones has helped resolve my
する/している problem (I think). I have one problem remaining though. Given
@Sonny365TANAKA's answer that 彼女は長い髪の毛です **is not** grammatical, if 田中さんは神妙な顔だ
**is** grammatical then what is the difference? Translating directly to
English, why can I say "Tanaka **is** a meek face" but I cannot say "She
**is** long hair". Both describe a person's features and both sound strange to
me.

**End edit**

> 田中さんは神妙な顔だ。  
>  田中さんは神妙な顔をしている。  
>  Tanaka has a meek face.

Describing facial expressions confuses me. Firstly because of the use of "is"
rather than "has" i.e. literal translation of the first sentence is "Tanaka
**is** a meek face". I can live with that.

Is there any difference in meaning/nuance between these two sentences. How do
I interpret している? Is it "is making", "has made", or simply "is/has".

Does the way I phrase it change depending on whether I'm talking about the
current state of the face or an enduring feature. e.g.

> Tanaka has a meek face (and it is always like that. It's just his character)  
>  Tanaka has a meek face (because he's just done something shameful)

Am I right that these issues occur with other aspects of describing a person?
For example I saw these two sentences in some example translations:

> 彼女は長い髪の毛です  
>  私の髪は長い

My instinct tells me that the second one is incorrect even though that is how
you would expect to translate it.




> Example-1  
>  田中さんの様子はどうだ？ How are they? (focus on the shot)  
>  田中さんは神妙な顔だ。 Mr.Tanaka is on his good behavior. (on his p's.)
>
> Example-2  
>  田中さんはどうしている？ Let me know how they are doing? (focus on the scene)  
>  田中さんは神妙な顔をしている。I'm not sure the proper English, but it could be "Mr. Tanaka
> puts his poker face."
>
> NG: 彼女は長い髪の毛です。  
>  acceptable: "彼女は長い髪の毛の人です。", OK: "彼女は髪の毛の長い人です。" or OK: "彼女の髪の毛は長い。"
>
> OK: 私の髪は長い。

