Legal Question in Criminal Law in California

In my book, that's premeditated first-degree murder. There's actually a lawyer here in L.A. who was the victim of such an attack (a rattlesnake, with the rattle removed, was left in his mailbox) but survived.

Search TVTropes.org for 'Animal Assassin'

Since you're the author and can make it whatever you want....

Yes, it's murder. Whether it's a gun, a knife or a deadly poisonous snake, your killer intentionally killed. That's murder. Because it was done in a very well thought-out way, it certainly appears premeditated and therefore first degree murder.

And as a twist - under California Penal Code section 190.2, murder by poison (your DA could make an argument that the snake's poison was just the same as arsenic) is a special circumstance, making the killer eligible for the death penalty.... if you want for your book.

Since the assumption in your facts are that the snake's poison is enough to kill someone, and it supposedly is known to be so venomous, replace the concept of "snake" with "bomb" and you have your answer. However, assuming you are going to make this a story that's more than a few pages long, we'll also assume you are trying to make defenses against the premeditated murder charge, and are looking for gradations of charges.

See the facts of a non-premeditated murder in People of the State of California vs. Marjorie Knoller. Her husband was convicted of involuntary manslaughter, and she was convicted of both the manslaughter charge as well as the second degree murder charge (a huge hit for a negligence dog attack case).