This topic -- the evidentiary status of the behavior of people in the courtroom -- is extraordinarily important (as Prof. Levenson fully recognizes) for both practical and theoretical reasons. The abstract of her article reads thus:
The American criminal courtroom is a theater where courtroom actors play out the guilt or innocence of the defendant for the jury to assess. Although one view of the courtroom is that of a controlled atmosphere where cases are decided based only on formal evidence, this view is undoubtedly unrealistic. Trials are affected by many factors, including the appearance and demeanor of the defendant. This article proposes an approach to deal with non-testifying demeanor evidence that occurs outside the witness box. Given the problems with having jurors rely on demeanor evidence, courts should be carefully monitoring the use of non-testifying demeanor evidence. Appropriate jury instructions should be given, including those warning jurors on proper use of such evidence.