Naturalists classify mambas as proteroglyphous snakes. This means the reptiles have fangs located at the front of their upper jaw bones that aren't very mobile. Whereas the timber rattlesnake (for example) can fold its fangs against the roof of its mouth, proteroglyphs — like mambas and cobras — can't follow suit.
Black mambas are normally shy around people. Given the opportunity, Dendroaspis polylepis will zip away from humans, mongooses and other animals that might try to hurt it.
Unfortunately, mambas are a common sight in rural farmlands, where they'll shack up in barns. Such proximity puts both mambas and humans in harm's way.
According to the African Snakebite Institute, a rearing mamba can lift up to a third of its body length off the ground. That gives the serpent a huge strike range.
Neurotoxins — substances that harm or impair the victim's nervous system — are a major component of black mamba venom. People who've been bitten by the snakes may experience paralysis, abdominal pain, slurred speech and other delightful symptoms like vomiting and vertigo.
In extreme cases, it can take less than 20 minutes for the mamba's bite to kill a human being. (Though some victims hang on for several hours before expiring.)
Needless to say, anyone who's been struck by one of these snakes should be immediately hospitalized.
The good news is there's an antivenom available. When properly treated, many victims survive. We should also note that black mambas sometimes deliver harmless "dry bites," in which they strike their target without administering any venom. No need to waste the stuff.