the chirping of other chicks and sounds of hen, encourage chicks to fight to hatch. supposedly. i have no proof, as i had put my cripple chook "clucky" by the egg, when the one piped and had started rolling around and chirping, but could just have been a flook, but they did seem to be talking to each other, and my hen did start to try to roll the egg under her, and tap lighter than she usually pecks, seeming to either help it chip its way out, or just curious (leading me to wonder if its not bad to help chicks hatch, as parents in wild supposedly do, as well as pet chickens).