A lizard is stretched out on a rock, basking in the sun. The skin on the underside of its neck throbs gently as it breathes. It is warm and contented.
At the slightest noise he will shoot off to hide under the rocks. You may be quicker than he is, but if you catch him by the tail it will come off in your hand like a ripe fruit off a tree.
It is painful for the lizard, but he would rather lose his tail than his life. About half-way down his tail there is a ring of muscle which is strong enough to break the back-bone when it contracts. So a pull is enough to complete the amputation. The tail will grow again at least once.
It is also said that the wagging of the tail-end can distract the attention of an enemy. And in fact it does continue to twitch for a few moments after coming off.