I went through a good number of interviews. So this is what I do usually.
If the recruiters talks directly to you, then you listen. According to what they say, you may nod your head, say some "ah!" or "oh, really?" occasionally, as needed. If some question pops up to your mind related to what they say, it is perfectly fine to draw their attention that you have a question, and then ask the question. In the end, a successful interview is a dialogue, after all. Both parties should ask and answer - just the interests are different.
In one interview, I was told the name of the city where the business was located, and I was not able to understand the name of the city even after the repeated it to me several times, at my request. I ended that part of the discussion by asking the recruiter to send me a short e-mail with that name of the city, so I can process it in my mind. They did. In the end, I got the job and relocated there.
If they happen to be talking between themselves, then you have nothing else to do, other than watch. That is, until they finish, and move on with the interview.
Bottom line: be natural, as if you were in any other discussion. Don't over-do anything.