What, pray tell, is going on in there?

First, the mayor's jurors reach consensus on one of 14 counts, but seem stunned and strangely discomforted when asked to disclose it. Two days later, a juror is whisked to a hospital complaining of stress. And after deliberations covering parts of seven days, the fate of D.C. Mayor Marion Barry remains unknown.

Equally unknown are the methods and passions of the nine women and three men who have lived and breathed the Barry case since their sequestration on June 18. That is exactly as intended: the Anglo-American legal system takes considerable pains to insulate juries from scrutiny of their labors.

"Nobody really knows how juries work, and nobody really wants to know," said one senior prosecutor here who spoke on condition of anonymity. "There's a black box aspect to it: the evidence goes in and a verdict comes out."

Details vary from case to case, but most juries have their unusual moments. The reason can be unsettling to those depending on the results: No one tells a jury how to decide its case. In short, 12 ordinary citizens are improvising -- doing justice, by their own lights, as best they can.

During 30 days of evidence and argument, every waking moment was structured for the mayor's jury. U.S. District Judge Thomas Penfield Jackson told them what to do, when to do it and what not to talk about in the meantime.

Everything changed after final arguments last week. Jackson gave the jurors an hour of legal instructions -- difficult, in parts, even for lawyers to understand -- then packed them off to the jury room to start their work. For the first time as a group they had no supervision, and no agenda to follow but their own.

"It's an odd process when you really think about it," said William D. Pease, a former assistant U.S. attorney. "You sit them through a trial and then try to teach them 300 years of common law in an hour of jury instructions. Then you let them go. They do some pretty bizarre things in there."

If the setup comes across as laissez-faire, said E. Lawrence Barcella, that's entirely "done by design."

"Deliberations are supposed to be purely the jury's function," said Barcella, another former prosecutor. "The whole thought behind the system is that they are the arbiters of the facts. You don't interfere with their deliberations, period."

The few indications available from the jurors in Barry's case -- most dramatically the hospitalization of juror Deborah Noel yesterday -- suggest a panel that may be divided and under some stress.

Drug possession, which makes up 10 counts of Barry's 14-count indictment, is among the least complex of criminal charges, and most of Barry's possession counts rely on one or two witnesses. Possession is the kind of charge that is tried and decided in a single day in thousands of local drug cases. Yet Barry's jury has struggled to reach a consensus.

The mayor's case, of course, imposes exceptional pressures on all involved. The jurors came into the case, by their own testimony during jury selection, with opposing and strongly held views. How they resolve those differences is entirely up to them.

There are jurors, every now and then, who come to blows. Others express their differences with less force. W. Gary Kohlman, a defense lawyer, likes to tell of a case in which a jury locked one of its members out of the room. And judges have a standard quip, only half a joke, in cases involving handguns: both the gun and the ammunition have been entered in evidence, the judge will say, "but I won't be sending them back to the jury room together."

The standard jury instructions, taken literally, suggest a decision-making method that matches the evidence against the so-called legal "elements" of every charge. But few juries work quite that systematically, and the law does not require them to do so.

"Most jurors, by virtue of their occupation, are not used to analyzing problems and engaging in the sort of deductive reasoning that lawyers go through," said defense lawyer Henry W. Asbill. "They may come about it in a totally different fashion than you or I might do. The safeguard is found in the fact that there are 12 jurors bringing various insights, various ways of life, various ways of reasoning. Hopefully they will reach the right verdict, whether it's for the right reasons, from our perspective as lawyers, or not."

Most trial lawyers have stories of jurors who made decisions for the wrong reasons. One prosecutor tells of a jury that persuaded a holdout to vote for conviction with this argument: "One lady said, 'Woodies has got a white sale on Thursday, and if we don't finish this thing up, we're going to miss it.' " Other lawyers say the approach of a weekend or holiday will speed a verdict.

Still others describe scenes of bargaining in the jury room, as if in a back-street bazaar. Unable to reach true unanimity on the merits, lawyers say, some juries will simply cut deals: a conviction here, an acquittal there, and a compromise struck in the end.

Federal rules make it nearly impossible to challenge a verdict by casting doubt on the methods or competence of the jury. Three years ago, the U.S. Supreme Court even rejected an appeal based on evidence of "rampant drug and alcohol abuse by jury members," including marijuana and cocaine, during deliberations.

"That's one of those results where lay people go, 'What?' " said the senior prosecutor. "The idea of it, I think, is that the jurors should feel free to discuss candidly without worrying that the content of their deliberations will be spread before the world."

Staff writer Elsa Walsh contributed to this report.