This idea apparently came from several people, including Violet, Lindsay and Danya, and it's a good one!
Presumably, our pups have lives that happen when we aren't playing them, as none of us can play 24/7. Some of the things that happen are tedious and everyday, and not worth thinking much on: It's fair to assume they eat, bathe, go to "work" or school as it applies, etc. But there might be things that happen between pups that, while not necessarily requiring a thread, are important to note for the sake of development. The important stuff should always be played out, but we know you can't always play everything, and sometimes you need a little nudge in the right direction.
One of the habits we mods are always trying to reaffirm to all of you is communication, and chances are you already e-mail or IM with other muns to discuss your characters' relationships. What this meme is all about is expanding on that, to better create a personal history that you can then use to better build personal development. To paraphrase Lindsay, "it's not intended to be a way of avoiding/handwaving actual threads but rather a way of kickstarting them and getting a better idea of where our characters stand with each other. It's a small island, and it's likely that a lot of our pups have interacted, maybe in little ways."
Create a post in your pup's journal where others can ask for or give details of interaction/shared experiences that haven't been played out, and then link that post in a comment here. The details can be silly or trivial (They see each other at breakfast everyday), or a shared anecdote (Remember that time when they got attacked by the angry parrot?), or the seeds of a bigger plot to be played out later. There's an example of a post
here, but you can format it anyway you like.