Never stare directly at the Winter Lantern, lest ye be frenzied.
Those who delve into the arcane fall all-too-easily to madness, and thick human blood serves to calm the frayed nerves of these inquisitive minds. Naturally, this often leads to a reliance on blood ministration.
The real twist is that Yayoi didn't kill David's mother, she stole his eye.
......yeah but I get the feeling Yin and Jin killed his mother instead, that mention of taking a woman hostage and her being tortured to death is too specific.