Easy way to get Brain Salad achievement
When You are in the safe room wait for the music that signals to you that the horde is coming and then close the door. The horde will try to break in but can't so they keep standing there. Take out your hunting rifle, shotgun, Assault Rifle, or Auto Shotgun and stand their blowing there heads off! Have fun killing zombies.
More tricks, tips and cheats for this game are right here - Left 4 Dead cheats
Comments for this hint