[ShankS]

slow or fast:
imo zombies should be slow, muscle decomposition and bodily functions are all reduced to a corpse like undead state. Their bodies seam to shut down and the only thing that they want is to feed on human flesh. With decomposed muscles and body parts, fast movement would be pretty difficult...no matter how much the zombie 'disease' had infected them.

If it is able to remove all thinking, consciousness and sane thoughts from a victim’s carcase, so that they feel no pain imo thoughts provoking the knowledge of fast movement would be nonexistent. Also, slow zombies give a much greater effect during a film, because of the slow impending doom for their victims.

killing one:
Since zombies do not appear to have any continuing brain functions, apart from minor instincts (see below) I feel that complete removal of a zombie’s brain would end its 'undead' life. However, as seen in many zombie films, gunshots to the head, some of which do not completely remove the brain or end with decapitation, still result with stopping a zombie.

imo as said, the only way to stop a zombie should be complete decapitation and removal of the brain, since there is still some form of basic instinct remaining in the brain. What I would like to see in zombie films is complete decapitation and any zombies that have minor injuries such as a small handgun holes in the head, to still be moving. Many scenes in films show zombies being stopped in their tracks by small arms fire, with a brain still intact, which would still be able to function in an unread state.

fire etc:
As for fire, I'm similar to you on this one, why a zombie would be more scared of fire than a gun I don’t know why. They’ve obviously retained some sort of fear to fire and not guns. maybe the idea came about as a sort of 'caveman' instinct...whereby fire has always been know as a danger and used for protection since the beginning of man on this planet.... think of cavemen using fire for protection and as a weapon to be scared of.

thoughts and tools:
Zombies could retain some form of mental instinct, locked somewhere within their brains. As Humans...the most intelligent life form, the decomposing of the body and brain would be a gradual process, as seen in many zombie films. A victim doesn’t necessarily become 'zombified' upon being bitten. Their body and mental state goes through a gradual transition from human to a 'moving' rotten corpse.

I suspect the same process would be similar to what happens to the brain. Everyday functioning, such as knowing how to open a door, use a toothbrush, or scratch your ass would be lost pretty soon, as these are things we do without thinking, whereas some things that get 'locked' into our brains during human state could be retained... but not necessarily everything, things like places we visit or a house we recognise could still be retained in basic form.

Also.... how do zombies know that human flesh is what they crave? The still are capable of retaining an instinct for the need to feed, why do they attack humans instead of raiding the fresh meat counter at the local supermarket....why don’t they eat each other, do they require human flesh for some reason that helps them retain some form of instinct??

rotting:
I believe that a zombie would continue to rot to the level where all natural human proteins and molecules muscles etc would be consumed. As evidently shown in zombie films, a zombie is infact 'dead' and the infection or whatever is within their bodies. Enables minor body functions to continue.

All human flesh would be 'taken over' to produce this 'undead' state where rotting stops. Somehow the process of natural rotting, such as in a naturally dead corpse, would no longer happen, because the infection could somehow 'preserve' the whole zombie features of the undead state.