I also concur with the advice offered. I have an fun anecdote:
I have not always been able to pursuade a willing and hopeful student to do
this. I have made a "wig" from aluminum foil and X-mas tree tinsell which
works wonderfully. One year I had a hopelessly talkative and enthusuastic
student with a buzz cut who was bitterly disappointed that he could not
volunteer for this demo. A "friend" suppested he do it with the "wig" on.
Without much forethought I helped him get set up. With him standing on a
stack of books and with starting V = 0, I turned it on. It did not take long
for him to leap off the books with a howl!!!! There had quickly built up
sufficient PD for sparking to occur between the wig and his scalp. It was a
short buzz cut!! It was quite a performance!!