The eggs in my homemade incubator just passed day 8. One of the eggs, which was fine and had a live, moving chick in it 2 days ago, now has a large dark streak near the air sack area and a hairline crack running perpendicular to it. I thought I saw a little bit of movement in there, but not even close to what it was doing a couple of days ago. Can a crack just appear out of nowhere like that? Did I do something wrong? What is the streak? Should I keep incubating the egg and give it a chance? I've read that cracked eggs generally dont hatch, but there's a part of me thats hoping I didnt see what I thought I saw and that the streak is somehow "normal". Thoughts?