I've been thinking about this recently as my knee has healed after a sharp encounter with my new plow. I was pushing the ATV out from the ditch (I had pushed the snow back a bit too far) and hit my knee on the edge of the plow blade. The resulting hit not only took off some skin (through my jeans), but caused the knee to stiffen up quickly. Now, it was not a serious injury, but I was concerned that it would give me the excuse my body wanted to avoid my reestablished exercise routine.
While it did hurt for the next several days (and still does if I touch the wrong spot), I was impressed with how quickly I healed, especially after it hurt quite a bit more on the second day. When I consider any robot that we might build, I realize that it might be more difficult to damage (like the Terminator), but it would also be significantly harder to repair. Our bodies use the food that we eat to power these magnificent machines that can accomplish a much wider range of tasks than any machine could, and do so for decades.
That's quite impressive.