Iowa Code § 624.14: Juror as witness — grounds to set aside verdict.

If a juror has personal knowledge respecting a fact in controversy in a cause, the juror must declare the fact of the knowledge in accordance with rule of evidence 5.606(a), and the juror may not testify in the trial of the case in which the juror is sitting. Proof of such a declaration may be made by any juror in support of a motion to set aside a verdict.