I'd guess because the air cell means there's a light spot. An egg isn't perfectly balanced, it naturally has one area heavier than another. When you turn it so that the heavy area is up, gravity means that the heavy area tries to go back down.
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I'd guess because the air cell means there's a light spot. An egg isn't perfectly balanced, it naturally has one area heavier than another. When you turn it so that the heavy area is up, gravity means that the heavy area tries to go back down.