Shoot at it until the game keeps going.
Laziest, most uninspired design I've seen yet in an RE game. T-Rex, Bull-Horse, Spider-Fly, all giant skyscraper sized demons that can be retracted back into the same six foot human being who retains all higher brain function. Seriously? Even for Resident Evil, that is ludicrous.
At least in previous RE's it was at least implied that mutation was a one way street. It has to be right? You are organic matter. You can't just pulverize deep tissue and magically restore it.
It's just shameless to me how badly Resident Evil wants to be Transformers. The main Boss literally just grabs heaps of flesh and tacks it on for extra fortitude like he's fucking Optimus Prime. Even the mutations look like transformations. I know I'm in a way describing Uruboros here, but at least that was just an uncontrollable growth with no rhyme or reason to it whatsoever. I could at least get on board with that.
Splitting your body up in blocks like you are a robot is just ridiculous.