I bought some eggs on eBay... Two started developing, one of which was in the incubator because it had a ruptured air cell (it started to develop and quit about half way through), the other was under a chicken hen. At three weeks, the egg under the hen was looking good. Day 28 came, no chick. I candled the egg real quick and thought I saw movement, but it could have been my eyes playing tricks on me. I was looking really close and if it was actually movement it was faint. I put the egg back under the hen (not easy to get it or put it back, the hen was very protective), and worried, I came in and looked in the sticky. It said 28 to 30 days. That made me feel a bit better... Day 29, went out to check, hen was still sitting on an egg. Day 30, same story. Today is day 31. I went to check, still an egg. I brought it in to the house to candle (I wanted a dark room). After staring intently for a while, I thought I saw movement. I finally decided that it was actually my eyes playing tricks on me so I took the egg out and gently broke it open. It contained a fully formed chick, yolk sac absorbed and everything, but it was dead. What could have gone wrong?