Aggressive thrashing when paired

[Dave Green]

So we put the black widow with a confirmed female overnight and the first day went by alright. We checked back the next day and the male was "gnawing" her back. Just sort of opening his mouth, putting it on her and removing it. It wasn't a defensive strike, they were both resting relatively still next to each other. Is this a sign of breeding? Should I be concerned? I'm separating them for now in case it was putting the female at risk.

Nine years of breeding ball pythons and I've never seen that.