What special characteristic makes a snake a viper?

Answer 1

All Vipers are known for the two venomous fangs in the front of the mouth. Most Vipers are short, stocky snakes and have broad heads to allow them to consume their prey. All vipers' coloration tends to be camouflage to their environment.

Answer 2

Vipers or Viperidae(the scientific family name) are all venomous snakes with a pair of hollow fangs that are able to rotate down from the inside of the upper jaw of the snake. The head is usually very triangular or arrow-shaped, and when striking(either in defense or for food) the jaws can open nearly 180 degrees to insure that the fangs penetrate the target's skin. Most have live births, and when compared to other snake species, vipers tend to be more sluggish.

Viper venom tends to be of the protein-degrading type that break down the cell walls of blood, muscle, and arterial cells, as well as causing extreme pain. Death is not common, except in those of small body mass or sick. The venom can cause extensive scarring, and even possibly amputation - but venom reactions very according to the specific species, age of snake, amount of venom, and the victim's own reactions. Older snakes will often NOT inject venom in a defensive attack.