Verb: The act of fucking without both partners having knowledge of the female being on her period.
Surprise menstruation while fucking.
Fucking so hard that it produces vaginal bleeding.
'Last night we were going hard like a couple of sex-starved crack fiends when Big Bessy surprised me with a redheaded stranger.'
'Yeah dude, she bled all over me like the motherfuckin' red seas had parted.'.