The first type of viviparous is the boa. Boa is a common name for a non-venomous, constricting snake. There are more than 40 types of true boas, including two Asian species that lay eggs rather than give live birth. These snakes are known for their large size and capability to coil themselves around their prey, killing it with crushing force. Another type of viviparous snake is the viper. Snakes in the viper family are venomous. They are known for their long, hollow, poison-filled fangs that they use to strike and kill their prey. Among the 200 species of vipers are rattlesnakes and copperheads, two snakes in North America that are often feared. Garter snakes, on the other hand, are non-venomous and are harmless. Also found in North America, this third type of viviparous is relatively small and can be handled, although they may secrete a foul smell from their anal glands and bite if they feel threatened. Of all the snakes in the world, only 30 percent are viviparous.