A: These questions are as old as Zombies themselves and for good reason; with all the different types of Zombies there is no definite answer, but we will do our best to shed some light on this puzzling situation.
The first thing to keep in mind is that not all Zombies actually eat human flesh, and the ones that do sometimes only eat the brain.
Some Zombies, like those from 28 Days Later and Berlin Undead (Type Two Viral), don’t eat so much as ravage human bodies. Their highly aggressive nature and drive to spread their disease often outweighs their desire for food. These Zombies, when eating, will stop feeding when their bellies are full, when fresh prey presents itself as a possibility, or the virus begins to takeover their victim.
Other Zombies, like those of Romero or Fulci (Type One Viral), will often continue to eat despite outside threats of harm. If left to their own devices these Zombies will continue to eat well after their stomachs have burst and can no longer contain the “food” they take in. Type One Viral Zombies will cease their gorging when the virus begins final take over of its new victim; this period ranges from minutes, to hours, to days.
Vodun and other psychological type Zombies may only attack you in a crazed state. Their psychological condition is so fragile that, if triggered, they may attack and try to eat human flesh (biting, tearing, and consuming as a crazed animal might) until they are removed, killed, sedated, or their victim dies.
Chemical Zombies, like those from Return of the Living Dead, are primarily after brains, not human flesh. Chemical Zombies eat continuously, never satisfied with any amount of “food”, and will only stop when destroyed, food runs out, or fresh prey makes itself available.
Currently there are no cases of Zombie cannibalism reported to have taken place… though that doesn’t mean it hasn’t happened.