Se me está descongelando el bistec
(My steak is defrosting) •
It's a way to indicate that someone is menstruating. You say this because when you defrost a steak (or any piece of meat) there's blood coming out of it.
"Hoy no iré a clase de natación porque se me está descongelando el bistec."
"I won't be on swimming class today because my steak is defrosting."