Grounded in American history and relentlessly claustrophobic, "Croatoan" traps Sam and Dean in a town full of people being infected by a blood-transmitted virus that makes them become violent. The hour is intense, and it showcases just how strong the bond between the brothers truly is as Dean refuses to kill Sam — even if he is infected. Even by Supernatural standards this is a dark episode that is designed to leave the viewer feeling uneasy long after it ends.