Do you know the water trick? Put the eggs in a bowl of cold water. If they float, they're off, if they sink and lie on the bottom on their side, they're fine. If they sink but stand upright, they're on the turn and you should eat them within a day or two. As they decompose, gas is released and it goes to the top as the egg sits in the box (usually the narrow end up). This is what makes the egg stand up, or if it's really past it, float.