Do you mean don't say something...that people can't hear?Don't day something...that people can't hear!
Yes, that's what I understood it to mean.The first thought that came to my mind when I read this is to not whisper something to someone where others around you cannot hear it. Somewhat like, don't tell "secrets," similar to what @MACKTEXAS mentioned.
Well, if you say something that people can't hear, it either means you're alone, or in a room with deaf people.
Either way, whatever you say won't matter. It's a moo point (Like a cow's opinion .... it doesn't matter).
That's good - I didn't think of it that way.Don't waste your time speaking silently to yourself!![]()