When not attacking, Common Infected are very vulnerable, usually sitting down, leaning on walls, or simply standing. If an idle Common Infected receives a non-fatal gunshot wound from a distance they will writhe in pain and clutch the wound with their hand. They are often seen engaging in bizarre activities such as vomiting, attacking inanimate objects, and fighting each other. In rare cases, one can be seen facing a wall and making mumbling noises, as if talking to itself.
The Infected appear to lack a sense of self preservation, as they will actively charge into flames, explosions, jump off from high buildings, and against superior forces of the Survivors and their weapons, even if they have encountered these things before. Due to loss of higher brain functions, they seem to ignore pain and damage even when their limbs are blown off.
They seem to have some grasp of their current situation, or at least how they feel; generally, idle Infected act physically ill, holding their heads and vomiting as they shuffle around slowly. Occasionally, one of the Infected who is holding their head may begin to writhe in pain, or they may simply lie down and sometimes die without being shot or punched. Common Infected are shown to have a primitive but working communication system with others, generally through grunts and screams. They are also shown to see the Survivors as something inhuman, or something of the sort, which may explain why they attack them- it may even be that symptoms of the Infection include immense hallucinations followed by adverse paranoia which leads them to attack nearly anything they see moving, including their own kind on various occasions. Anatomy breakdown is shown in the case that if a Survivor would step on a sleeping zombie, they will immediately die.