Cassiopeia's Auto Attack/Particle Questions

Never really thought about it until now with 6.9 on the cusp. I know twin fang is the manifestation of a snake exposing its green poison fangs when casted, and her q is a mini green cloud explosion.

1. Cass's auto attack is a green snake thingy? Does she literally throw snakes at you or??
2. Miasma is purple, and the poison indicator is purple. Doesn't that contradict the use of the green particles?
3. Is there a difference between purple and green poison? They seem to have the same effect as a DoT.