Hello! I am new and I have seen my eggs always seem to be rocking. I don't know their hatch date as I rescued them. I'm guessing they are on day 27??? Anyways they have rocked for the past 4 days and I saw a duckling today that was like yanking at the air sac as if nibbling... Is this normal because it seems to me as if it is struggling to open the air sac to make its internal pip. I also see it pressing against the air sac and when it nibbles the air sac it pulls it hard as if its desperate to open it... Is this normal???? Plz help!