Menstruation affects half of the world’s population during their lives. But it’s little understood. Here are five surprising thing you may not know about periods.br br Subscribe to BBC Ideas br Made by Angel Sharp Media in partnership with @oxforduniversity. br br br br Do you have a curious mind? You’re in the right place.br br Our aim on BBC Ideas is to feed your curiosity, to open your mind to new perspectives, and to leave you that little bit smarter. br br So dive in. Let us know what you think.