The journal club picks a paper to discuss, often using crowdsourcing to select something people are interested in. Everyone logs into Twitter at a specific time and has an online conversation with people from around the globe. Someone may facilitate and use pre-selected questions, but there's also time for open discussion. You can string many tweets together, so you can basically write as much as you want.

Most journal clubs meet once a month for an hour, but the nice thing about Twitter is that the conversation is saved. So, if someone wants to comment the next day, the participants will see those responses whenever they log into Twitter. That's important because participants are from different time zones. Having the conversation publicly recorded could be an issue for some people, but I think scientists and clinicians aren't shy about asking questions and critiquing papers, even publicly.