My big female BP always wagged her tail when she hunted. Like a cat about to pounce. She didn't do it fast, just a slow little back and forth, back and forth, until she hit her mouse. It would stop while she ate, then with the next mouse, back and forth, back and forth.

It was funny to watch, I never knew a snake would do that. I'm not sure if yours is something different, since it sounds more agitated than what mine did.

Gale