Michonne moves so that Penny's between herself and the Governor, and the Governor begs Michonne not to hurt her, holstering his gun and then laying aside the gunbelt. Penny is a surprisingly effective human-shaped shield considering she's three feet shorter than the target. Michonne watches the Governor in horror and confusion, but a moment later, the point of her sword comes bursting out of Penny's mouth. So much for the shield. Without bothering to pick up his weapon, the Governor rushes Michonne in blind rage (spoiler!) and disarms her, commencing a rather savage fight whose highlights include Michonne strangling the Governor with her scabbard and the Governor bashing her head against the wall before smashing it through the side of one of the fish tanks. When he tries to pull her free, she pulls down several of them with her, so there's water and biting heads all over the floor on top of everything else. She gets in an elbow and goes for her katana, but he grabs her before she can reach it, so instead she pulls loose a shard of tank -- cutting her own hand in the process -- and sticks it into his right eye, then goes the extra mile by breaking the point off inside. He lies there screaming and crying and Michonne raises her sword again to dispatch him, only to hear a second screamed "No!" from the doorway.
This time it's Andrea who has a gun aimed at her, and Michonne's sword draws up short. "What have you done?" Andrea whispers in shock. They slowly circle each other, weapons pointed at each other's faces, until Michonne's at the door, at which point she lowers her blade and walks out without a word. Andrea goes to help the Governor, but is brought up short by the heads in the tanks and on the floor. But he looks so pathetic cradling his re-dead child with a chunk of glass still sticking out of his ruined eye that she crouches down to comfort him. And also because she's a moron.
Carl leads Tyrese's group into the anteroom outside Cell Block C, by which time the bitten woman appears to have died. "I'll take care of it," Carl says, holding his gun so that the giant silencer on it nearly touches the woman's forehead, even while she lies on the floor and he's standing up. Sasha asks who he is and who he's with, and Carl says they can help them. "But first thing's first." Tyrese declines, saying they take care of their own, and he pulls out his clawhammer. The bitten woman's husband and her grown son hold each other off to the side while Tyrese raises the tool over Donna's bandana-covered face, but before he swings it they're distracted by how Carl has just shut the door and locked them in there. Sasha gets pretty upset, demanding to be let out, but Carl doesn't budge, telling them they'll be safe in there with food and water. And I assume that our people have some other way to get outside from the cell block. Beth and Hershel are visible to the new people, but keeping mum. "Back away from the door and let the man go," Tyrese tells Sasha, so clearly someone already respects Carl. Probably helps that he didn't know the kid a few months ago. "Look around you. It's the best we've had in weeks. His house. And we've got other things to do." He tells Carl they don't want any trouble, and they get back to it. Beth asks Carl, "Shouldn't we help them?" "I did," Carl says. His transition to bad-ass is nearly complete.