Tex. R. Civ. P. 327

As amended through August 21, 2020
Rule 327 - For Jury Misconduct
(a) When the ground of a motion for new trial, supported by affidavit, is misconduct of the jury or of the officer in charge of them, or because of any communication made to the jury, or that a juror gave an erroneous or incorrect answer on voir dire examination, the court shall hear evidence thereof from the jury or others in open court, and may grant a new trial if such misconduct proved, or the communication made, or the erroneous or incorrect answer on voir dire examination, be material, and if it reasonably appears from the evidence both on the hearing of the motion and the trial of the case and from the record as a whole that injury probably resulted to the complaining party.
(b) A juror may not testify as to any matter or statement occurring during the course of the jury's deliberations or to the effect of anything upon his or any other juror's mind or emotions as influencing him to assent to or dissent from the verdict concerning his mental processes in connection therewith, except that a juror may testify whether any outside influence was improperly brought to bear upon any juror. Nor may his affidavit or evidence of any statement by him concerning a matter about which he would be precluded from testifying be received for these purposes.

Tex. R. Civ. P. 327