Hello, Luna. They explained to you about how to do locked comments, too, right? You can write a comment on a public post if you use the 'I solemnly Swear' language, using the special ink, and only those of us in the know can read it, not even the person who wrote the original post, if that person doesn't know the secret.

Now that you know, you can go back and look at the older locked entries, too.