By using default meanings, couldn't the title be shortened to: 

> 
> 箱を探った。
> 
> 
> 

1. Isn't `の中` so obvious, it is assumed to be the location you searched? If I were to search **under** the box, then I *would* write `の下`?
2. Isn't `手で` so obvious, it is assumed to be with what you searched? If I were to search with my **foot**, then I *would* write `足で`?
3. In *formal written* Japanese, shouldn't you try to shorten your sentences as much as possible?
4. Is the following correct usage of `暗黙了解':

> 
> この例では、`の中`も`手で`も暗黙了解です。
> 
> 
> 

I am only talking about *formal writing*. Unnecessary words are naturally used in every language in conversation.