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The Codd bottle was designed and manufactured to enclose a marble and a rubber washer / gasket in the neck. The bottles are filled upside down, and pressure of the gas in the bottle forced the marble against the washer, sealing in the carbonation. The bottle is pinched into a special shape to provide a chamber into which the marble is pushed to open the bottle. This prevents the marble from blocking the neck as the drink is poured.
Output:
why did old bottles have marbles in them