I hate the fact they (the characters) are very slow to react. If someone falls while being chased by zombies that person keeps sitting on the floor waiting for someone to drag them aside or to be bitten by zombies.
If they see anyone among them who just got bit or is infected they wait for full 5-10 minutes for that person to completely turn into zombie and for it to run after them when they can actually pin the person down when he is just twisting and turning, you know when he is the process has just begun.
Namra before turning into a zombie keeps sitting/ standing like a statue and does nothing, literally nothing even when everyone around is struggling/ fighting zombies. The only time we see her doing anything is when she proposes "going to the roof and distracting zombies with music" plan.
Even when she is bitten by a zombie she doesn't experience the "twisting and turning" like other people who turned zombie.
And when she turns into a zombie even then she doesn't fight or saves anyone from other zombies who are attacking them except in one or two scenes where they are fighting a bully.
She can easily walk among other zombies and get things for the group but she doesn't take any initiative.
On-ju keeps sitting and waiting for the bully to completely climb up and land on terrace when she had a chance to attack the guy.
Namra being a zombie/halfsy can pick/break door locks like the other girl who turns halfsy but again doesn't do much when they are trying to break the terrace door to take the chopper. She literally stares at her hand for almost 4 minutes when she realises she is capable to fighting the bully and zombies being a halfsy when we see them fighting the zombies in the stairway to terrace.
Firefighter father is wearing a black protective suit while running out of the quarantine facility to get to his daughter, and he removes his helmet right when they are firing on him which otherwise would have been a shield and even then the army is not able to take him down. We see them firing and no bullet hits him in head where they are actually firing and instead it hits him somewhere in the torso.
He had a complete chance of escaping zombies with kids when they are in the ground surrounded by zombies but he chose not to leave and sacrifice instead for no reason.
None of the people bitten by zombies are shown turning into halfsies but these three kids in the whole city.
In the end all the zombies chase the drones playing that frequency but Namra again doesn't respond to it like other zombies or infected people.
Su-yong gets bitten by the bully still he doesn't turn into halfsy like namra.
Namra doesn't bite anyone even when she feels the urge to do so yet she stays alive (zombie being) despite not eating any food (human), as we see her enjoying born fire in the end on the school terrace.
All stupid kids/ people who are acting unwisely and running around are saved and survive and those who actually put their lives in risk and try to save such stupid people, end up loosing their lives.