During a Zombie-pocalypse a quisling is any person who has become so physiologically disturbed that he/she subconsciously convinces him or herself that they are one of the walking dead. A quisling will imitate a zombie perfectly and will attempt to feed on a normal human should it encounter one. A quisling's bite is NOT infectious. Because a quisling is not truly one of the undead, a quisling can be killed like a normal human, not just with a head shot.
"Shit dude! It bit me!"
"Don't worry about it bro, it was only a quisling. You'll be fine."