Travel around the world to visit some of nature’s most incredible snakes: vipers, and find out which are the most dangerous. -- As of 2021, there are 368 species of viper worldwide. The name comes from the term viviparity, which means giving birth to live young. Vipers are often highly venomous, with two hollow, extra long fangs that unfold into imposing weapons when the viper prepares to strike. So, which are the most dangerous? Andrew Whitworth travels around the world to visit some of nature’s most incredible snakes. Lesson by Andrew Whitworth, directed by Billie Baxter.