Clickers are some of The Last of Us' most terrifying Infected, as their increased strength and resilience make them formidable foes for Joel and Ellie. Formed during the third stage of the cordyceps infection, Clickers have been completely taken over by the virus and rely on echolocation to navigate their surroundings by producing clicking and croaking sounds that alert them to any nearby threats or hazards. The fungal plates on their heads provide additional protection to their head and brain, making them even deadlier, as the head is typically one of many other Infected's primary weak spots.
Source：https://www.cbr.com/tlou-clickers-gameplay-guide/
