Only the closing of the opening need be heard for the ear to distinguish the sound.(original) Question: Does the "the closing of the opening" refer to the same sound as the "the sound" in the original? I don't think so. I understand the original this way: The sound from the opening is different from the sound that the ear discerns. Perhaps the noise coming from the opening is too loud and masks this special sound. Therefore, only when the noise from the opening is turned off can the ear distinguish this special sound. So the original perhaps can be rewrite as: People need hear only the sound of the closing of the opening, they will manage to to distinguish the sound (from other sounds). I doubt what I imagine the above about the original, because without further context, It's hard to be certain the exactly meaning of original. I'd like to hear what's your view about the exact meaning of the original.