Add a new NPC zombie called 'The Screamer' (Siren) that spawns in towns/banks. She alerts the horde by screaming if damaged or disturbed, waking up all sleeping zombies in a large radius. She has 0.5x HP of a normal zombie, runner's speed, and normal damage. Her appearance includes ragged denim clothes, a white tank top, long hair, and yellow glowing eyes. When screaming, the player's screen shakes and blurs slightly.