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Do you mean following and unfollowing in some sort of rapid succession?

Yes, I think that’s exactly what I’m talking about; the interval between the two actions would correspond to a letter in Morse code

I suppose over a long enough time interval where you can absorb the lag the user would receive.

You’d also need monitoring as the networks done reveal exact time stamps on follow / unfollow.

You could build a little toy that automates follow and unfollow and monitors and if two people ran that they could communicate.

Or they could just DM :)