A thorn fights another thorn - the very best!!! :P :P :P :P

The proverb is about using some one- a wicked- against another wicked. The phrase- A thorn fights another torn- does not indicate that some one is using. If two wicked persons fight each other on their own without being used by someone, your phrase would be correct.

I think the proverbs lose their appeal if these are rendered literally and their beauty lies in figurative imaginations. Why a thorn - any object for that matter which is not endowed with mobility or initiating actions on their own need agency of humans to perform it. Here the suggestion of 'use' is subtle and needs to be explained from that perspective!!! I can readily refer to one of 'one stone killing two birds' to illustrate my point!!

Is it 'killing two birds with one stone' or 'one stone killing two birds'. ?

You are right but there are some proverbs which are based on figurative interpretations!!! A rolling stone gathers no moss!!!

This is 'personification' - a figure of speech. There are different ways to say a thing. How someone uses a phrase depends on his style.

Similes, metaphors, allegories are all parts of our expressions which lift our language to a surreal level. If I use ' a lion 'thunders' instead of 'roars' its impact is terrific. Roaring is a matter-of-fact expression and 'thunders' suggests so many possibilities!!!

In Sanskrit there is a proverb 'Sathe Sathang", be foxy with a fox!! :lol: :lol: