I'm amusing myself so much imagining this version of PHM where Rocky learns about menstruation.
Rocky's an engineer, not a biologist. They have a reasonably informed person's understanding of Eridian biology, but they're learning all sorts of wild things about human biology just by hanging around Grace.
So, okay, humans are squishy bags of water. Seems impractical but you don't get to choose your evolutionary trajectory. This means Grace is constantly taking in water, and also leaking it out, to maintain her internal water homeostasis. But, for something humans are constantly doing, she is so weird about it. Taking in water is something she'll do whenever and wherever no matter who is watching (gross), but leaking it out is something embarrassing and private?
Things Rocky has learned about human liquid management:
She leaks water out of her face (normal and fine, just embarrassing and private and she doesn't want to talk about it)
She leaks water out of her middle (normal and fine, just embarrassing and private and she doesn't want to talk about it)
She can leak blood out of absolutely anywhere (NOT normal or fine, a sign of injury that needs to be addressed right away, but she is not embarrassed or private about that at all??? She cut her hand on a xenonite tool while working and it started bleeding and she treated this as a minor inconvenience, but was cheerful and even excited to show Rocky what blood looks like and explain what was going on. Rocky actually wasn't concerned at first because Humans Be Leaking but that's how they learned to be concerned, despite Grace not being terribly concerned? It was confusing. Grace bandaged it up in the public workspace and explained blood and injury and it did make sense: something that is supposed to be on the inside falling out of a cut in your body is not a good thing. And blood is Supposed To Be On The Inside. They can accept this without too much trouble although now they are anxious about Grace being so fragile and able to leak all her crucial Inside Water so easily.)
New discovery: she leaks blood out of her middle (normal and fine, just embarrassing and private and she doesn't want to talk about it)
I'm imagining a distressed Rocky going Grace is bleeding! Grace is injured question??? And Ryland going. Uhhh no this is normal. This is expected. This happens every... hang on... 720 hours, approximately. It's called a period. Cause it happens periodically. Never thought about that before.
Rocky is somewhat skeptical. Grace is bleeding but it is not a concern, question? Grace isn't lying to Rocky question? And Grace has to be like no genuinely this is just a thing the human body does. In fact if I wasn't doing it that would be a much, much bigger concern. Because it would mean I was either starving or the name of this mission just became terrifyingly literal.
Rocky: ... Grace making joke question?
Ryland: yeah I'm making a joke.
Rocky: Rocky not understand joke.
Ryland: it would take a lot of explanation that's not really relevant honestly.
Rocky: joke was funny question?
And then Rocky asks to see the blood and Ryland gets to experience what exactly she asked Rocky to do when she wanted to watch them eat.