Countess Elizabeth Bathory, 1560 - 1614, serial killer, "Blood Countess", "Blood Lady Of Cachtice", tortured and killed hundreds of girls and young women, possibly over 600 [convicted of 80], bathed in the blood of virgins in order to retain her youth, said to have had a cage with razors and spikes hanging on the ceiling and a chair beneth it where she would take a "blood shower".
Mayo probably uses past knowledge and harvests said blood for those purposes.