Menstruation (mammal)
Menstruation in mammals is the shedding of the uterine lining (endometrium). It occurs on a regular basis in uninseminated sexually reproductive-age females of certain mammal species.
Yanomami women
Up until the time of menstruation, girls are treated as children, and are only responsible for assisting their mothers in household work. When they approach the age of menstruation, they are sought out by males as potential wives. Puberty is not seen as a significant time period with male Yanomami children, but it is considered very important for females. After menstruating for the first time, the girls are expected to leave childhood and enter adulthood, and take on the responsibilities of a grown Yanomami woman. After a young girl gets her period, she is forbidden from showing her genitalia and must keep herself covered with a loincloth.