Eggs
Is an egg lighter or heavier when cooked? An experienced cook is experienced in eggs. There are "new laid" eggs which are fresh and "fresh" eggs which are not; there are "cooking" eggs which are liable to squeak. Eggs are safe in their shells, and think you don't know whether they are fresh or not, or whether they are raw. Any egg can be thrown out of a first-floor window on to the lawn without the shell breaking; it falls like a cat, right end upwards, and this is not a boiled egg, either! You can tell that because it will not spin on the table, so it must have been a raw egg. A cooked egg would spin.
To tell a stale egg, you will see it is more transparent at the thick end when held up to the light.
Fresh eggs are more transparent in the middle. Very bad eggs will float in a pan of water.