Why do lizards tails move after they've been cut off?

A geckos tail will continue to move after being detached from the body in the same sense that if a humans arm was completely torn from the body, it would continue to twitch and move. These are the nerves within the limb. At the base of the animals tail, is cartilage, which has to ability to retract from the body when in danger. Within the tail are fat reserves, calcium, nerves etc.. The tail is still a living part of the animals body.