Many animals are able to regenerate in some way or other.
One of the most noticeable examples of regeneration can be seen in salamanders. Whole, fully functioning, limbs can be recreated if needed. As soon as a limb is severed the regeneration starts, the wound heals and then a growth of de-categorised cells forms. These de-categorised cells are much like human stem cells as they can become any type of cell they need to be. Over the next few days or weeks the limb grows back using the de-categorised cells; the limb is fully functional with nerves and blood vessels, an exact copy of the original limb.
Some regeneration is seen in mammals with the re-growth of antlers, finger tips and ear holes. Human children up to the age of ten have been known to grow new finger tips if needed as long as the wound is not covered and human livers can fully regenerate as long as they have 25% of the original tissue.
The idea of regeneration is often used in fiction, with comic book heroes such as Super Man, The hulk and Spiderman all able to regenerate their wounds.
It is a very interesting idea that animals can re-grow limbs, and that humans can re-grow finger tips, if only we could use these ideas to re grow human limbs and organs; I suppose if we did more stem cell research we might actually get somewhere, who knows.