After injury, some animals like salamanders have the ability to completely regrow their limbs. Mice and humans have retained a sliver of regenerative ability. If you damage the end of your finger, as long as there is a bit of nail left over and the wound is not stitched up, it will grow back.
In our lab, we are trying to understand why we can regenerate a fingertip but not an entire arm. If we can understand how the tip of the finger regenerates, we can use this knowledge to develop therapies to regenerate other parts of the body.