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Soundless
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Inside the belljar, the bell can still be seen to ring! If the rubber bands hanging it are good enough, few vibrations will pass up them to the glass (to be heard). Letting the air back in allows the sound to be heard again.
WHY? With very little air inside - perfect vacuums are impossible even with the best equipment - the bell has little chance to pass its vibrations to gas molecules. Even if remaining molecules do pick vibrations up, there is virtually no chance of them bumping in to others.
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