Blood and mating behavior??

[Sarah Conte]

Hey all: Two of my gerbils, Bianca and Lucentio, are newlyweds.  (I just got Bianca last night)  They've been getting along positively great!  In fact, they didn't even bicker in the slightest.  After sniffing each other and some minor posturing, they settled right in and slept together.  Today I came home and there was blood all over the walls of their cage.  I looked them both over very carefully and while there was blood all over his nose, feet, belly, and both of their genitals, I couldn't see any specific sign of biting.  Nor are they fighting now.  In fact, she's looking like she wants him to mate her.  I think that they might've been mating before I came in.  Can it be possible that the blood is a result of the mating?  I've never seen it before.   Thanks, Sarah