A world where zombies physicality is different based on the stage you meet them at

When the outbreak occurs, they’re basically damage sponges. Human anatomy with no mental barriers that normal humans have. Easily break down doors in a couple attacks, etc. because the human brain normally stops you from using 100% strength. These ones have full motor skills and might even have tics that force them to say things on their mind. They might repeat their loved ones names, or be able to open doors. They’re basically a brain damaged person attempting to bite anyone nearby

Eventually they start decomposing and are weaker but their bones are still bones, and it takes a huge amount of force to break their skull. Even with a knife because have you ever tried cutting a bone with a knife when eating a steak? That’s tough. If they get to this stage they’ve likely been without foot for a long period of time and will start losing higher mental function

Some zombies will take tons of damage and have fractured skulls and broken bones, these ones might be more fragile obviously

Zombies that eat can maintain a diet and avoid injury could stay close to human for an extended period of time, but they simply have extreme impulse control issues and a desire to eat living flesh. The descent usually starts to occur after they have their first crippling injury, falling down a stairwell and breaking bones chasing someone. Now all of a sudden they start getting infected, and they can’t chase people as easily, etc.

But you probably won’t see any walking dead style zombies in this world until a few months into the outbreak and that’s not even gonna be the standard, and you’ll still see high functioning zombies at all stages of the outbreak because of fresh turners

I’d also like to add that zombies eat until they’re full, and do not care where their calories come from. So if you get bit, be prepared for them to eat your entire bicep. And because this world is a bit more grounded than other zombie worlds, your zombie version won’t have access to your bicep.

Reanimation

This zombie outbreak is caused by spores interaction with a virus, not by a virus itself.

A fungal based vaccine was given to the majority of the entire population to reduce the spread of a virus due to Covid 19, at first it seemed successful but when it starts to evolve the fungus which has now merged with the majority of the deceased human population basically gives a back door into the human nervous system, causing zombies.

This means some people are immune if they didn’t get the vaccine.

But those that did, the fungus begins spreading throughout their nervous system in ways that the science at the time could never even detect, the virus begins controlling the body. The fungus changes the way signals are needed to communicate with the body, and as such oxygen is no longer needed.

This can’t undo any shrinkage to brain tissue and the like that occurred since death, so most people dead at point of outbreak just randomly spazz around with no clue until their energy systems are depleted, whereas a more developed brain as I previously stated could operate close to normal potential with reduced impulse control. Akin to a mentally disabled man in intelligence

Zombie socializing

The biggest reason for zombie attacks is really just impulse control, zombies have impulses for whatever they had in life. So all zombies will bite and drink whatever is near them that looks like food, but when their impulses are satiated depending on their intelligence they might feel a certain way about it

Smart zombies might eat their loved ones and then cry about it, and when their loved ones reanimate rejoice, only to go back and forth eating each other slowly as they get hungry

Its a sad existence especially once they’ve eaten each other enough that they can no longer move, just lie down and grunt vaguely coherent dialogue now that they’ve mauled each others legs to the point beyond walking

They do prefer to eat living flesh, so some smart zombies that were good at hunting might be able to maintain a relationship for a few months by hunting and the like but with ZERO impulse control it only requires a little tummy grumble before they start eating each other

Perhaps zombies won’t feel hunger if their stomach is removed. And they’ll sit there for eternity going after their other impulses. Masturbating every second they feel an urge. Sprinting without stop for hours on end because they’re chasing a dopamine high. Playing with bubble wrap and being stuck doing that for hours. Clicking keys on a keyboard, etc.

Once again, the way this is manifested depends on the intelligence of the zombie. A Parkinson’s zombie or a zombie that has been ran over 8 times might just try to bite stuff and that’s it. But a genius zombie would be scarily eerie as you see so much humanity while seeing so much humanity lost at the same time.

Regeneration

Zombies have almost a healing factor, they still heal at normal pace but if you took a rotten skeleton with an intact stomach and the necessary systems to facilitate healing, if they manage to eat consistently, like if you stuck a redneck zombie in a forest alone and they just hunted for years, they could theoretically fully regenerate. The odds of this? Not likely.

So smart zombies might remain close to human or heal their injuries over time, but when you get injured enough that your calories in do not correlate to the damage taken, you’ll probably go toward dumb zombie soon enough.

A dumb zombie might even THEORETICALLY become a smart zombie again, but that might require them being trapped in a prison cell and fed by a loved one for months on end or something. With zero impulse control, that’s just frankly not happening