Back in Episode 11 of the Berserk anime, Casca and Guts fell from a high cliff into a river. Later, Guts found Casca suffering from high fever, so he decided to warm her body. While undressing her, he saw something (as I saw) like blood flowing down (I couldn't understand from where), then he said:
Now I understand. Must be hard, being a woman
What did Guts mean when he said that?
I don't think she was having periods, but then what else could it be specific only to a woman.
If you read the manga and watch the second film it's much clearer that she has her period and that it's menstrual blood.
The anime couldn't show sexual organs which is why it's so vague. I didn't understand when I first watched the anime either.
Hope that helps!
This panel hints that she was having menstrual cramps before the battle started. She is complaining about them happening while clutching her abdomen.
The entire chapter (and the next several chapters) are full of references about her health and discussion about a woman's place on the battlefield. She was clearly menstruating.
periodsas the reason is because in the scene at 19:32, something like blood was shown flowing down in zig-zag(forgot the correct term) way, but the source of the blood wasn't a sexual organ of course (as I interpreted the scene) . Even if I consider it was a sexual organ, it certainly can't create a flow path the way it was shown in anime.