@Greengirlkate, they are very fast. There also small. They might even go to the barrier from the bottom or top so the survivors can't hit them. 3 reasons why survivors find it hard to kill them.
OH JUST SHUT UP ABOUT THE COMPANION SAVING BUTTON! Just press [esc], click save and quit, go on your profile and your companion will be up again. Like taking hand grenades from a baby zombie. :p