Observers are silent Members, and unless told so, the participant won't know anyone is watching. Observers cannot voice chat with each other or the Moderator, however all observers and the moderator can chat with each other, as well as take notes, which will be time-stamped=glued to the moment in the recording when it was made.
So Observers are not able to interact with the Participant, because Participants don't know that Observers are present in the session.
A team member can also take over Moderation capabilities from the current Moderator, and once that member has taken over as moderator he/she can of course voice chat with the Participant. However we recommend that the original Moderator clearly informs the Participant about the moderator switch before doing it.