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There is a tiny air pocket inside eggs, and over time more and more air passes through their porous shells and into the egg. As more air enters the egg, the air pocket grows larger, making the egg more buoyant.  If the egg lays on its side on the bottom of the bowl, it is at peak freshness.  If the egg stands upright on one end but is still touching the bottom, it is aging past its prime but is still safe to eat.  If the egg is floating, it is not a fresh egg. This does not necessarily mean it’s bad or unsafe to eat. You should test the egg by cracking it open and looking for (or smelling) signs that it has gone bad. As the egg ages and moisture and carbon dioxide escapes through the shell, the yolk and white begin to dry out and shrink, and the air pocket in the egg becomes bigger. A larger air pocket gives the egg more room to move around inside the shell and create a sloshing sound.  A fresh egg should not make much, if any, sound when you shake it.  A sloshing egg only indicates that the egg is old and does not mean the egg is unsafe for consumption. The integrity of the egg will lessen as it ages, so it won't hold together as well as a fresh egg. Notice if the egg seems to spread over a wide distance on the plate, or if it stays relatively compact. An egg that spreads or seems a little watery has a thinner white and is past its peak freshness.  If the yolk is flat and breaks easily, the egg is old.  If the yolk moves around easily, this means the chalazae (the thicker strands of egg white that hold the yolk in place) have weakened and the egg is aging.  Look at the color of the egg white. A cloudy white indicates a very fresh egg. A clear white means the egg is older (but may still be edible).
Place the egg in question in a bowl or wide glass of cold water and see if it floats. Hold the egg up to your ear and shake it, listening for a sloshing sound. Crack the egg open on a plate or in a large bowl and check the quality of the yolk and white.