You know and I just want to address here that using blood from any source is a very powerful tool. Blood is the VITAL source of all life. You can use someone else blood to maintain contact with them...meditation/astral ways....also cursing/healing them....etc. YOu can use animal blood as a way of shapshifting//astral work...etc.
working in the veterinary field, i throw away vials of blood every day. i never even thought of using them. its already collected and no one gets hurt