Groups of people having conversions can often make closed circles which seems to exclude new people joining the group. This was observed by Eric Holscher (@ericholscher on Twitter) at many a conference so he proposed The Pac-Man Rule as a way of conversing groups making it obvious that they were ready for new people to join in the conversation. He has written about the idea here. The "hidden agenda" behind conference making this idea "a thing" is to try and make conversing groups open, welcoming, and inclusive.
Dylan Beattie (@dylanbeattie on Twitter) has made a short (21s) animation to show the idea: