Original: While most colubrids are non-venomous (or have venom that isn't known to be harmful to humans) and are normally harmless, a few groups, such as genus Boiga, can produce medically significant bites, while the boomslang and the twig snakes have caused human fatalities.
Simplified: While most colubrids are non-venomous (or have venom that is not known to be harmful to humans) and are normally harmless, a few groups, such as genus Boiga, can produce medically significant bites.