Hi,
That's actually been bothering me lately.
I was waching a tv show which mentioned some snakes actually being poisonous as opposed to venemous owing to their diet.
But my google-fu is seriously weak and I cannot find any actual scientific literature to back it up.
I did find this on answers.com;
Kind of threw me for a loop.Venomous snakes include several families of snakes and do not constitute a formal classification group used in taxonomy. The term poisonous snake is mostly incorrect - poison is inhaled or ingested whereas venom is injected. (There are... two examples - Rhabdophis sequesters toxins from the toads it eats then secretes them from nuchal glands to ward off predators, and a small population of garter snakes in Oregon retains enough toxin in their liver from the newts they eat to be effectively poisonous to local small predators such as crows and foxes.)
dr del