You can "candle" the eggs; hold them in front of a bright light. A flashlight will do. Once they reach a certain stage, they will move. When they first form, you will see the silhouette of what looks like a red spider; it's a clump of cells with blood vessels to it. This will turn into a duckling and almost fill the egg. When the ducklings are getting to hatch, you can hear them inside the egg, calling for their mother. Don't help them out of the egg; the struggle to get free is what gets their hearts pumping well.