It doesn’t even have to be a zombie, just a survivor with double personality, thanks to the Cataclysm horrors. To make it less OP, maybe a survivor infected by the fungus, suddenly coughing?
Damn, even just a common NPC with a flu in a city would be a problem 
…a Schizofrenic NPC? .-.
The ability to recognize blueberry bushes at a distance(different bush color, perhaps?), depending of Perception and Survival.