 Brooks designed World War Z to follow the " laws " set up in his earlier work , The Zombie Survival Guide ( 2003 ) , and explained that the guide may exist in the novel 's fictional universe . The zombies of The Zombie Survival Guide are human bodies <unk> by an <unk> virus ( <unk> ) , devoid of intelligence , <unk> solely of consuming living flesh , and cannot be killed unless the brain is destroyed . <unk> will eventually set in , but this process takes longer than for an uninfected body and can be slowed by effects such as freezing . Although zombies do not tire and are as strong as the humans they infect , they are slow @-@ moving and incapable of planning or cooperation in their attacks . Zombies usually reveal their presence by moaning . 
