A colubrid's body is almost completely covered in scales. Most colubrids are not venomous and are normally harmless. A few groups, such as genus "Boiga", can produce medically significant bites. In addition, the Boomslang and African twig snake have both caused human fatalities. The venom-injecting fangs associated with venomous colubrids are almost always in the back of the mouth, in contrast to vipers and elapids. 