Counter example for all snakes are poisonous

A Counterexample is a statement that contradicts the given proposition. The proposition given above is that, all snakes are poisonous. The counterexample would be, not all snakes are poisonous. One characteristic that will enable you to identify if the snake is nonpoisonous is their pupils. The pupils of poisonous snake resemble to that of a cat's; oblong shaped with sharp edges. Whereas, nonpoisonous snakes have round pupils. Examples of nonpoisonous snakes are  Python, Anaconda, Eastern Ribbon Snake, and Bullsnakes.