How can you tell a bad egg from a good egg? Just grab a cup of water and toss it in there. Good eggs sink to the bottom and lay flat, indicating that they are still fresh. An edible egg that is no longer fresh will sink to the bottom but stand on its end. If you come across an egg that you think is no longer good to eat, it will float at the top of the cup of water. Throw that out, as a bad egg will give you a nasty case of food poisoning.