First: Sending stones are pairs. So I am assuming you are breaking this restriction and all are considered paired.

Second: Sending stones grant comprehension of your message to any creature with the stone with at least 1 Int (all creatures). So you now have a universal translator laying about in the world (Universal as even allows you to speak to cats and dogs). Also you have given everyone the ability to silently communicate with nearby creatures. As using an object to cast a spell eliminates all components of the spell (V,S,M) and the receiver hears it telepathically.

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