You suddenly start your period. The demon brothers notice changes but don't say much about it. It's not their place to ask. However, Mammon pulls you aside.

Mammon: "Oi. Did you, ya know, start? Do you need anything? I don't have any Grimm, but I'll beg Lucifer or Levi so I can help you."

He seems genuinely concerned, which is odd in a way due to his goofy nature.