Edinburgh scientists have said that when a woman looks into a man's eyes and gets hooked, he most probably has large pupils, as women tend to be attracted to such men.
Edinburgh University study's scientists, who found that the attraction starts just as women are approaching their most fertile time of the month, believe that it could be because it indicates that the man is sexually interested in them and available for mating, reports the Daily Mail.
Pupil size made no significant difference for the rest of the menstrual cycle, according to the study published in respected journal Personality And Individual Differences.
To reach the conclusion, photographs of six equally attractive men were presented to a judging panel of ten women. But for each man, three versions of the photo were produced, with the pupils large, medium or small.
The pictures of the men were then jumbled and put into pairs for the women to rate. Volunteers recorded their age, whether they were using hormonal birth control, the date of onset of their menstrual period preceding the test and the length of their menstrual cycle.
The study's analyses revealed that attraction to large pupils shot up four days before day 13 of the menstrual cycle, the usual monthly peak in fertility.