the last of us: the infected

Runners are the first stage of the Infected who have recently entered their transformation. Since the eyes are first targeted by the fungus, runners have poor eyesight, but maintain many human instincts. For example, their moans are still human, just like their overall appearance. However, a way to tell them apart from normal survivors is their lambent red eyes. Their body language is sluggish while they are passive and makes it seem as if they are trying to resist the fungus. Sometimes they do not attack at all, even when right in front of them. These non-aggressive runners will only attack if attacked first or when an object is thrown at or near them, thus losing control. This is described to be like a "sneeze" like the developers say in a demo, where the host will find it hard to control when a sneeze will occur at any moment and when you are about to sneeze, it is hard to stop from letting the sneeze go through. Runners are confirmed to be able to attack in packs flailing their arms trying to trample the survivor. 

Stalkers are the second stage of the Infected. They have the vision and speed of Runners, although are more similar in appearance to Clickers. The most notable trait that defines the "Stalkers" is the beginning of fungal growths on the head and face, the development of pseudo echolocation, and their discretion when chasing a victim - they will strafe and take cover, eventually closing in on the victim, hence the name "stalker". Stalkers are the fastest of the infected to spot a survivor as they will spot them usually before a runner will even have a chance to.

Clickers are the third stage of the Infected that have had prolonged exposure to the fungus. By this stage, the infected possess strength that significantly surpasses the average human, making them deadlier- at the price of being completely blind due to the exposure from fungus in its face. However, Clickers are able to maneuver through areas by utilizing echolocation, which produces intense clicking noises to locate prey and sounds, much like bats but in a far more crude version, not able to locate prey unless right in front of them. Clickers appear less human than Runners, with faces that are skewed and scarred by fungus developed from their infected brains. Clickers are dangerous and much more aggressive than Runners, but no longer resist the fungus because their humanity has been diminished. When provoked, a Clicker will immediately enter into a "berserk mode," aggressively flailing its arms.
 

Bloaters are the fourth and final stage of the Infected and developed extreme brute strength. Bloaters take the longest to develop making them the rarest of the infected. They are guarded in thick fungus that effectively doubles as plate armor. Due to this protective covering, they can withstand multiple hits from weapons such as the Shotgun and Hunting Rifle, and even hatchets and machetes making them extremely tough to eliminate. Bloaters are extremely aggressive, but are rather slow-moving causing them to be more predictable than other infected. Like Clickers, Bloaters 'see' using echolocation to locate and trap a survivor as the fungus has completely deformed their face and blinded them, however their echolocation is a lot cruder than the clickers. If a Bloater grabs a survivor, it will forcefully rip their jaw apart through brute strength; there is no way to defend yourself if grabbed like you can with a Clicker, so use extreme caution when fighting one. Bloaters will throw balls of spores from their own body as a weapon, which disperse on impact, making a cloud of spores. Their spores are not infectious.