Looks good, very nice sense of form. I have only minor critiques:
The shoulder bite has the upper and lower jaw imprints too close, it looks more like a leech bite than a human/zombie bite. Human jaws are hinged pretty far back from the teeth, so when they open wide enough to chomp on a shoulder, the space between the upper and lower jaw imprints would be pretty big.
With how healthy-looking the zombie is everywhere else, I don't think it really fits to have the skin right on top of the ribs like that. Since he still has pretty juicy abs, then there should at probably be tendons for those to be attached to, and probably some trace of the oblique muscles. I think an easy "fix" would be to just remove the dark dithered shadow where the ribs meet the abdomen, which makes them look like they're sticking out behind the muscled areas. If they just smooth transition with only the red shadows, I think it'll look more like the abdominal muscles are layered on top of them, and the obliques are gone.