But poison, in any case, isn't a physical attack. The card Poison is a spell. If you can have a Poison spell, you can have a spell which poisons.
Also, I forget exactly what the discussion was, but a while ago I had a discussion with many people on this board about the mechanics of scorpions and at the time I was the only person who was saying that the poison was a physical attack, rather than a separate non-physical attack.