it is called pasty butt. you have to keep it cleaned off or it may close over the vent and it can't go poo and it can kill the baby. you can soak their butt in warm water if it is bad and they will let you. I just wiped it off with a warm wash cloth. You can put a little bit of mineral oil on afterward to keep it from sticking. If you get it wet, put it under a warm light or gently blow dry it. The chick can't get chilled.