He can't afford to make a sound now. Can't afford to let you so much as wince in pain either.
".. sh, sh, sh, I know.. I know.." he mumbles, his words barely above a whisper, his palm covering your mouth just in case. There's walkers surrounding you everywhere, with little chance of their dispersing or of your escape. It's a miracle he managed to shove the two of you in this godawfully tiny closet right in the centre of this chaos, anyway.
"Not. A. Word." he mouths, his arm keeping your back pressed to his chest, holding you in a loose half-nelson to conserve space. He understands it's tough for you to not cry out from your injury —having been shoved into a sharp knocked-over pole earlier that went straight through the guts— but damnit, if you make a noise now, you're both dead.