What venomous snake is known for the dark black inside of its mouth?

The black mamba is the venomous snake known for the dark black inside of its mouth. Its common name is not a reference to black body scales: adults are usually gray, olive, brown, or gunmetal, while the mouth lining is dark bluish-gray to nearly black.

The species, Dendroaspis polylepis, is native to sub-Saharan Africa and was formally described by Albert Günther in 1864. It is Africa’s longest venomous snake, commonly reaching 2–3 meters, with exceptional specimens reported above 4 meters. It lives in savanna, woodland, rocky country, and some forests, and can climb as well as travel on the ground.

The black mouth is part of a defensive display. When threatened, the snake may gape, hiss, raise its head, and spread its neck slightly, making the dark interior conspicuous. This is often confused with the idea that the snake itself is black, or with the black coloration of some cobras. Its venom is chiefly neurotoxic, and untreated bites can cause respiratory paralysis, but the snake generally avoids people unless cornered or blocked.