-strength- some zombies are weak an some are strong even if they look alike. Some take 3 hits others take up to 18. I've done serial tests with different weapons to figure out which is the most effective way to take out zombies. An honestly I don't think there is a method behind the madness. I think there strength is randomized an in my tests most of them take 5-6 hits plus which is outrageous. It's rare to find one that goes down quick.

• gun fire- zombies being shot with a range weapon are similar to the effects with a melee weapon but not as severe. Some take 3 rounds an drop others take a full clip at point blank to go down.

-alerted range- being alerted by gun shots I've shot an had some swarm me an then hide on a building to seeing others couple houses away still walking around aimlessly as if they never heard it. While others are coming from nearby towns to the shot.
-agro range- Another issue is there agro range some zombies I'll be crouched down walking right behind them an they won't notice me others will be a couple houses away an notice while crouching. Or I'll be cutting one up an then one from wayyy down the street will get agro an come at me.
-walking thru walls- I've had incidents where I shut a door an felt safe knowing ive blocked the entry ways just to see a zombies runs right thru it.
-floating- seen it more then once an not just right above the ground but roof level of farm houses. Unable to get aggro'd. I tried. An didn't notice me no matter how much noise I've made. Walking around as if he was on the ground.
-spawn- I've killed all the zombies in a small area maybe 3-4 houses so I could loot in peace just to have them spawn right back after searching the second one. Or have killed the zombies in a small military camp to be able to check the tents in peace just to walk out an have them all right there waiting for me to step out. I've also had ran into areas where there shouldn't be many zombies but find there's an obscene amount for such a small area.
-hitting- more often then not the zombie will rush me an hit me as he runs by then run back to hit me as he goes by again all while I'm swinging an not hitting him at all. Or runs around me hitting me as I just try to get a hit in. My hits sometimes just go right thru even at point blank. An there's lands every time. Sometimes the zombie hits me 3 times an I'm knocked out others it's takes more. Or when I take on 2 at a time( death wish) an it takes them 2 hits to knock me. Where other times I've took on 2 an survived more then 2 hits from each. With gear or just starting fresh is the same.