hormones... when we have more estrogen we go for the more masculine type. and at our time of ovulation, women also tend to be more attractive in the eyes of men rather than the other days of our cycle. it also changes the quality of our voice, etc. we are just not aware of this changes.
Thank You for that excellent explanation. You are right, about men knowing when a woman is ovulating. A woman also becomes more sexually active during time of ovulation, just from my own observation.
Women also emit pheromones during ovulation that men are reactive to , tho they are oblivious to it.