A joint snake is a mythical creature of the Southern United States

Southern United States

The Southern United States—commonly referred to as the American South, Dixie, or simply the South—constitutes a large distinctive area in the southeastern and south-central United States...

, the myth likely having spread elsewhere.

Supposedly, the snake can break itself (or be cut) into pieces and will reassemble itself. It is said that if a piece of the snake is taken and the pocket knife used to cut the snake is set down in the place of the snake's piece, the knife will join up with the whole of the snake. The myth is probably based on legless lizards

Glass lizard

The glass lizards or glass snakes, genus Ophisaurus, are a group of reptiles that resemble snakes, but are actually lizards. Although most species have no legs, their head shape and the fact that they have movable eyelids and external ear openings identify them as lizards. A few species have very...

 than can regenerate their tails after they are broken off. Such lizards are often called joint, or, more commonly, glass snakes. May also be a reference to the Hydra in Greek Mythology

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

.