Haven't you heard the legend of the field hand who chopped at a rattlesnake with a sharp hoe, cut the snake's head clear off and flipped it up into his face, fangs first?
My Great Grandfather allegedly lost an employee that way.
Great Grandfather Hall was an interesting man, well regarded for giving paying jobs to freed slaves. He wasn't an MD but he had medical books and kept a medical bag in his two wheeled buggy and was all the doctor the country folks had.
Nervous energy can keep a viper's head venomous and dangerous for up to 1-1/2 hours after separation. Cut it off, use a shovel and dispose of properly