Is an animal more poisonous than a plant?

It depends on the type of plant and the type of animal, although there are many types of poisonous animals e.g the dart frog.

There are only two snakes in the world that are poisonous to humans and other animals. As in if you ate them they would make you ill or kill you. That is because they eat poisonous animals (frogs etc) and retain the poison in their flesh. Don't confuse poisonous with venomous. Venomous snakes make and store their venom and kill or maim by biting or spitting. In the majority of cases their flesh is safe to eat.