Answer: The old man on the jury noticed marks on the side of her nose.
The old man on the jury, played by Joseph Sweeney, comments that the marks on the side of her nose could only have been caused by eye-glasses. She was a vain woman who did not wear them in court. She would also not have worn them if she was tossing and turning trying to get to sleep. For the juror played by E.G. Marshall this allows him to declare that he has a reasonable doubt, and to change his vote to "Not Guilty". It is perfectly possible that the woman got the marks from wearing sunglasses, or that she was long-sighted. However, the woman's eyesight has been called into question, and this shifts the balance of possibilities in the accused's favour.