28 Weeks Later/Nightmare Fuel


 * Don. Robert Carlyle is good at creepy anyway, but him as an Infected was nightmarish, and that's not an easy thing to do. The scenes where he's first turned and what he does to Alice are horrifying, and the fact that he seems to retain some very basic reasoning just makes it worse. He's not a mindless, murderous creature like the Infected in the first movie--he's still very murderous, but he's got enough marbles left to actively hunt his children through London.
 * The Infected, yet again. But worse, as they seem to have some sort of basic intelligence. Not enough to avoid things like snipers, but enough to ambush you, or kill you in even more exciting ways.