When something bad happens to your body. Say maybe you fall on your arm in a bad way, the ‘stick’ of your arm (the thing that makes it straight), might break. The way that it becomes not broken is very interesting. Once the break happens, blood forms a thick area around the break. In this blood tiny things that help your body stay good, clean the arm-stick and makes bad stuff go away.
Over the next couple weeks, more small things form a soft ball around the break. Once this happens, over time even more tiny things slowly add rock-stuff to the soft ball and then the soft ball becomes hard stick-stuff. After that, the stick is made back into stick form and the area where the ball was is cut around the edges to fit the form it had in the beginning.