[dementedmongoose]

Okay, I'll argue this in the order your problems came up, TDK:

1: How do you get smarter without amazing powers of regeneration? You learn. I didn't mean that a ten year old zombie will know more than it did before it was turned just by virtue of its age, it can just access more of what it already knew.

2: Gangrene was an example. There are countless infections that, left unchecked can trash your brain.

3: Finally, I'm using the propane tanks as an example, yet again. But yeah, there's a lot of suspension of disbelief. Zombies are my prime example.

And finally, about the Professor and the zombie virus. The virus was based off of both the RE virus and some conjecture between myself and one of my friends. The basic run of our conjecture was that if a corpse sets up rigor mortis prior to reanimation, it will have to either lie still until rigor wears off, or break every joint it moves and risk near paralysis. A person who turns from a bite, but doesn't die from bloodloss first will recover their knowledge much more rapidly than someone who died before turning, and will regain full use of their limbs more rapidly, since very few cells are killed in the process of turning a living body than there are cells dying from oxygen depravation as a corpse. Again, I'm not explaining it well, but the basic idea is that zombies don't regenerate, but they do reanimate dead cells, so while your brain may be completely dead before reanimation, the cells can be brought back to life.

Cellular division is slow, since otherwise zombies would be insanely huge, what with no cells dying. A disembodied zombie hand is still alive, but it has no commands coming from the brain, so it'll never move again, but I'm not quite sure how fast it'd rot. I think that makes sense. Complain if it doesn't.