(a) At the Trial. A member of the jury may not testify as a witness before that jury in the trial of the case in which the juror is sitting as a juror. If the juror is called so to testify, the opposing party shall be afforded an opportunity to object out of the presence of the jury.
(b) Inquiry Into Validity of Verdict or Indictment. Upon an inquiry into the validity of a verdict or indictment, a juror may not testify as to any matter or statement occurring during the jury’s deliberations, or on any juror’s mind or emotions or mental processes, as influencing any juror’s assent to or dissent from the verdict or indictment. Nor may a juror’s affidavit or any statement by a juror concerning any matter about which the juror would be precluded from testifying be admitted in evidence for any of these purposes. However, a juror may testify: (1) whether any outside influence was improperly brought to bear upon any juror; or (2) to rebut a claim that the juror was not qualified to serve.