Two of my friends have been dating for quite some time, and I am truly happy for them, however, whe they have sex together, they do it while using their nails and their teeth to take chunks out of one another. When they finish, blood is everywhere, and it's leaving permanent scarring. They are showing no ill effects from this, but, could this be dangerous,should I get them to stop?
It sounds to me like it's something more immature than anything, as if they want everyone to know they are having sex. Obviously, there is no need for that type of behavior, no matter how good the sex is.
One thing I can share with you to consider is that human bites are very nasty and can cause infections.
Second, becoming addicted to that type behavior for sexual pleasure and arousal could cause problems for them down the line.
I am no expert by any means, so that's just my honest opinion.