In horror fiction, a zombie is a human ghost or spirit "somewhere between living and dead, puppeted by external forces". This book explores real zombies in the natural world: organisms that lose control to exploitative parasites as seen in a tropical wasp that paralyses a cockroach, leading to its consumption by the wasp's young. This concept may extend to humans being susceptible to 'zombie bugs'.
We had this thing about, No, they're not zombies. They're infected. We wanted them to behave in a different way physically, but they also weren't undead. They could die and they will die, but so will you if they catch you.