Imagine explaining to aliens what a period is:
Alien: why are you bleeding?
Me: What?
Alien: your bleeding, what happened, are you okay?
Me: oh yeah this just happens
Alien: What??
Me: yeah, once a month young females on our planet bleed from our uterus’s because we need to get rid of the unfertilized egg. It’s annoying.
Alien: … ok then
*a month later*
Alien: here are some pads and some chocolate.
Me: thank you but why?
Alien: it’s your once a month bleed.
Me: Oh. Yeah mine isn’t like that.
Alien: what do you mean?
Me: mine is very irregular, so I don’t get it once a month most of the time.
Alien: so when is your next bleed?
Me: oh no one knows for sure
Alien: not even you?
Me: not even me. You can get it predicted but it’s not exactly accurate. Like at all
Alien: Damn