A period is a woman's favorite thing to do when she's not pregnant, or at least that's what people think. They do not enjoy talking about stuff that gets them angry during their PMSing time, or they will use their razor-sharp claws to kill you with one scratch to the chest, ripping out all your organs the first try.
Periods have influenced woman since the beginning of time, but when they weren't treated fairly back in the middle ages, people said that the women just had to deal with it somehow when they were having their period.
What happens? Edit
Well, what happens during a period? What do I look like, a construction worker? I don't know; go ask a woman lol