Causinae

The Causinae, commonly known as the "night adders", are a subfamily of venomous vipers found in sub-Saharan Africa. The family is monotypic, since it only has the genus "Causus". There are six species.
The night adders can grow to around 60 to 90 centimeters (24 to 36 in) long. They are usually dark gray, light gray, light brown, or black in color with gray or black blotches.
Even though they are called the night adders, they are usually active at day, but some are active at night. When they are attacked or disturbed, they usually coil up and start hissing at their enemy to scare it off. Some may raise their head and neck off the ground, and with their tongue sticking out, move froward like a the Cobra does. 
They eat mainly toads and frogs, but there are reports of some night adders eating almost everything they can find until they are completely unable to swallow any more food.
Reproduction.
All night adders are oviparous, which means they lay eggs. This is unusual for most vipers, because most vipers are viviparous, they give live birth. They lay around two dozen eggs at a time. These eggs take around four months to hatch, when they hatch the hatchlings are 4-5 inches (10-12.5 cm) long. 
Venom.
The night adders have very big venom glands, which are around 10 centimeters long. But even though the venom glands are big, the adders don't always use their venom on their prey. The venom would kill the prey fast enough, but they usually seize their prey and swallow it.
When someone is bitten by a night adder, the venom does not spread around the body, and only causes swelling in the place of the bite. There have been no reports of deaths by night adder venom.