I need grammatical explanation for this sentence "its poor torn mouth an O of agony". It's weird to me that there is no verb in this sentence, I think it would be like "It's poor torn mouth formed an O of agony"
The boy seized it and tore the bait from its mouth, ripping it horribly.
'Oh!' I whispered, covering my own lips.
It got a lot worse. The fish was flopping about frantically, its poor torn mouth an O of agony.
From "Buried Alive" by Jacqueline Wilson