All this wondering gets him stabbed in the heart. Rin's still kind of in denial about Shima, wondering if he's being controlled or something. Shima is taking advantage of this in battle. The zombie goes after Rin and no one else because Rin is the biggest source of energy in the room and therefore most delicious to zombies I guess. I like that Suguro is sitting in front when everyone rides Kuro, like goddang it I don't care how dire the situation is it is MY TURN to ride in front this time (I imagine is what he was thinking) Rin falls, Shima goes after him, Yukio gets everyone on Kuro to escape/regroup
