Its zombies....How does someone coming back to life eating human flesh make sense???
So the speed thing didnt bother me at all.
the theory is, when they reanimate their decaying flesh causes them pain, so the fresh flesh acts like a pain killer. it makes some scientific sense. consuming your blood would be like a transfusion.
but the WWZ ant zombies are ridiculous. they're worst than the powerhouse zombies in "I am Legend."
Walking dead has a nice concept of a viral infection causing the reanimation, which is plausible, if they are between life and death. I've never read the comics. Shane reanimated very quickly. I don't think they are completely brain dead when the transformation process starts. Brain death is the key. that's why the walking dead is so big on brain/head injuries before reanimation.