why do girls have periods?

[hehehahaheahea123]

any girls know y?

is it because they get horney??/

i really need to know cause my gf is acting weird..

[Rain]

....................................are you for real? or you just acting stupid?

[Xegra]

Because they deserve them.

[AnnD]

hasn't your mom already told about it. If not just ask her

[RachelG]

It's a fertility thing. The womb builds a lining to support an egg, when it's fertilised. If the egg isn't fetilised, the lining is flushed out the body - i.e. a period.