I had a female who wagged.
Not fast like yours, but slowly, like a cat about to pounce. I never knew snakes could tail wag period unless they were rattlesnakes. But every single feeding, before she would strike, she'd back into her strike curve, and her tail would start to wag. Back and forth, back and forth, back and forth, them BOOM no more prey!
I always laughed to see her do it.
Gale