I read in the Bible that drinking blood is forbidden, and I found out it has a reason. Genesis 4:10 - "And He said, 'What have you done? The voice of your brother’s blood cries out to Me from the ground." Hear me out.
Context — Cain murdered his younger brother, Abel, out of jealousy, and when God (subtly) called him out for it, he sassed Him and He clapped back at him (with verse 10).
This verse basically means that in our blood, there is genetic evidence of our entire lives in it, from birth to death — every single thing that happened in our life is encoded in our blood, just like a transcript. It's the entire essence of our soul.
Now, if you consume blood, you mingle the life of another with your own and it may affect your thoughts, your mind, your soul, and that person becomes a part of you, and there will always be traces of them remaining.
And OF COURSE I've been using this in Blood in Snow ever since 2023, but I wanted to give a proper explanation for Bill's odd or unlikely behaviour. He's not bipolar, although he does have his issues (clearly apathetic, depressed, and narcissistic), BUT it's because of Rachel's blood.