Character Design: Zombie Pre-facial Expression

Below are two pages of designs for my zombie character, as an agglomeration of flesh the skull isnt specifically fused to the mass and has a gaping mass around where the mouth would be.  

I was given some guidance which helped me to think about transitioning from a more cartoon style too a more horrific and menacing look, below are a series of  drawings to help me come up with the final idea of how the monster could look, it was suggested instead of having a gaping hole there doesn't even need to be a mouth at all and instead a twisted rib cage could sit in a position to which it looks like a mouth and has another purpose. 

 Below are two ideas of my own to help try and define how my character looks, i will begin to work more into 'fleshing' it out.