When a beardie egg is ready to hatch it usually begins to sweat a bit [ tiny drops of water form ] , then it collapses as the baby starts to break out. The yolk sac does nourish them and is usually absorbed before hatching but some babies DO hatch with a yolk sac attached, some fall off quickly, others can take a day or more and be the size of a pea. There's no way to tell while the dragon is in the egg if the yolk sac is absorbed though. And yes, you can shine a penlight on the egg while in a dark room and see the shape of the baby but not the actual yolk sac. If you do candle them be brief because the strong light can stress them.