Why did she had her head shopped off?
Getting your head chopped off was reserved for nobility. The common people were usually hanged or worse. An executioner had to be good and the person being executed had to remain still and keep their neck stretched out so the executioner could give a clean stroke. It was customary for the victim to pay the executioner for his work and forgive him before he did it. By the historical record, Anne Boleyn got a quick death (nice and clean). There was another lord who ended up getting more than six strokes. After the third one he jumped up and berated the executioner saying he could do a better job himself! Since he was still conscious and able to talk after three strokes, I have to agree with him. That was shoddy work. As far as the laws of the day, we are not in a position to judge. ‘Nuff said.
