My Black Australorp has been sitting on some various chicken eggs. It is now day 24 and we've only seen movement from one of her eggs. I believe the egg in question has pipped internally, due to a large dip in the air sack. From what I understand, a chick must then pip externally, then move in a circle to break the shell. Well, this egg doesn't have any external pips. It does look like it's trying to unzip, however. Should I try assisting yet, or is it too early? What are some indications that the chick is preparing to hatch? We have not heard any peeping or scraping of beaks against the shells. Is this normal?