In your games, are all your adversaries capable of surviving 9 points of stress, or are you using fewer for smaller creatures, or maybe even more for bigger creatures. It seems to me like a zombie bear could take more damage than a zombie human, could take more damage than a zombie box turtle.

In my games I've tweaked the zombies stress tracks depending on how well my pcs are handling them. At the start of the game my zombies have the full 9 points of stress but as the game goes on and my players get over the shock and get used to zombie killing I lower the number of stress points to 6 but start having larger groups attack them to make up for this. It's your game so ultimately you decide how strong you want your npcs to be.

Alright. That makes sense. I was t sure if there was a rule I missed when dealing with smaller critters. For example, if a rat swarm has 9 stress, and one or two days break off the swarm to attack someone else, it seemed like they shouldn't get 9 stress as well. Maybe some negative dice for being harder to hit, but not as resilient as the whole swarm.

I'm planning on trying to run a one off and was wondering this very same thing.

My interpretation was a sliding scale depending on what type of zombie(s) the part encountered, with more decayed zombies running around 3 or 4 stress while "fresher" zombies would be 6 or more.

It depends on how they attack the zombies.

This weekend one of the guys put a zombies head between a table and the wall after which the other kicked the table as hard as he could... I gave him 3 black dice for it but he did manage to do it. The zombie was killed outright...

SPLAT!

I also determine the condition of the zombies attacking my players, are they fresh (9)? Are they a little weathered (6)? Have they been exposed to harsh environments or decomposition (3-4)?

I had this exact same question. The pre-made Ghouls, Zombies, etc., in the rulebook have Dexterity, Vitality, and some info, but it does not indicate how much stress it takes to kill them...

I've kept zombies at 9 stress if they have all their body parts/are pretty much whole; but the more broken up/worse for wear they are, the less tiers they have (three tiers, two tiers, or one).

I'm keeping the "doubles on successful attack roll = headshot/brain destroyed" rule, but also declaring that aimed shots to the head require 3 successes on top of any negative dice issued to instant kill the zombie. The player declares beforehand that he's aiming at the character's head; if he does this, but rolls only 1 success, then his attack misses entirely.