welcome to left 4 dead 2,you’re in a apocalyptic world full of zombies or infected of all types like the basic ones and the special ones although there are ones with more reason like two girls zombies in specific

Spitter: growling while roaming the streets looking at you while growling

Witch: crying and running around the streets looking for you while crying

They are in the streets searching for you to catch you because they need love or affection they feel alone and sad