Which pair does NOT fit the classification shared by the other three?

Three of the pairs join an animal to the sound it makes: the lion roars, the horse neighs and the frog croaks. The odd pair gives a body part instead, since fangs are teeth and the sound a snake makes is a hiss. The pair looks at home because fangs are as characteristic of a snake as a roar is of a lion, but the group is built on sounds.