What does viper venom to blood? (amazing video)

Everyone knows that snake bites can be deadly, but exactly what happens when snake venom comes into contact with human blood?

This video shows a Russell viper being milked by a snake handler who then collects the venom in a glass jar.

One drop of the potent yellow venom is then extracted and mixed with a vial of human blood.

Within thirty seconds, the blood has turned into a solid block of jelly, demonstrating the venom's phenomenal blood-clotting abilities.