There are the experts on the witness stand, and then there are the experts in the jury box.
In the quest to understand what happens in the jury room, one might easily get lost in a single resource: the Arizona Jury Project, which I mentioned yesterday. To gauge the effect of a new rule allowing jurors to discuss evidence as the case went along, Arizona allowed law professors Neil Vidmar of Duke and Shari Diamond of Northwestern to videotape juror discussions in fifty actual trials between 1998 and 2001. Vidmar and Diamond have been publishing the lessons from the resulting tapes in a series of very good articles.
Relying on each other, not you
Obviously there's a lot of material here, perhaps best absorbed one lesson at a time. Here's one, chosen because it documents something lawyers often don't anticipate about juries: they rely heavily on each other's specific life knowledge, treating each other essentially as mini-experts, in their discussions. In the article Juror Discussions During Civil Trials: A Study Of Arizona's Rule 39(f) Innovation, Vidmar and Diamond detail what exactly jurors talk about behind closed doors. (While they are focusing on pre-deliberation discussions, their description would be accurate for all of the the mock trial deliberations I've seen.)
Vidmar and Diamond explain that when they get to the substance, jurors' conversation includes both "fact exchanges" and "inference exchanges." (The section I'm working from starts at page 58 in the web version of the paper.) In "fact exchanges," jurors try to get straight what the evidence showed. In "inference exchanges," they are clear on the facts, and are discussing instead what they should conclude from it. In debating these inferences, Vidmar and Diamond tell us, jurors "draw on their own experiences and information," their "personal knowledge of the world," and they seek information from each other in addition to simply saying what they think. That makes sense, but what I think many lawyers don't expect is how frequent this kind of discussion is. Vidmar and Diamond talk about juries where up to 61% of the exchanges in which jurors were seeking information were these "inference exchanges."
The point: you have mini-experts in the box, and the others will look to them for guidance on how to interpret everything from whether a faxed contract is valid to whether a burn injury can take that long to heal.
Changing the subject: Watch The Jury 101
On the other hand, maybe you should be happy if you simply know that the people in the box are the ones you started with. It seems that last week, both lawyers and the judge in an Oroville, CA courtroom got through the first ten minutes of the morning's testimony in a firearms case without realizing that one of the people in the jury box was not a member of the panel. 
(Apparently one juror was late on the same day a different person showed up mistakenly for jury duty; someone counted heads and put 15 people in the box without calling names.)
It's hard to say how long this would have gone on. Only when the missing juror called to apologize did anybody realize she wasn't in the courtroom. Now there's a lesson we didn't know we needed to learn: if nothing else, at least check to see that the faces are familiar.
(Nametag photo by the queen of subtle at http://www.flickr.com/photos/queen_of_subtle/313134750/)
