You are right, of course.
A superficial cut in a vein would flow that much blood, but I doubt if they cut into the corpus cavernosum or the corpus spongiosum.
It could be real blood, however. Blood is a funny thing. 50 cc of it makes such a mess that you cannot believe that whoever lost it is not bleeding to death.
But you talk about your safe sex and body fluid precautions...
This could get you hepatitis A, B, non-A or non-B, C, HIV, veneral disease of all sorts... I guess that catsup or perhaps tomato juice would be the only thing that I would have anything to do with if I were doing any sort of pics...
People....!

A-1
