Hello everyone. In order to practice, I am currently starting to read a book ( Обломов ). I read very slowly and try to understand everything, especially the use of cases, since, some of you may know, it is somthing hard for me at the moment

so I encountered this sentence :
" Мысль гуляла вольной птицей по лицу "
which, i know, roughly translates to " thought, like a bird, walk freely on his face " ( something like this, sorry, I have the french translation of the book, so I am translating this too, I hope you understand )

What I don't understand is the use of the cases.

вольной и птицей are in instrumental form ; and

лицу is in accusative form ( If i'm not mistaking )

anyone could explain me why they are used like this ? thank you in advance