I find the human body to be quite the incredible thing. Just think about it: as I type, I am not jamming my fingers onto the keys, I am just using enough force to depress the key. I am not thinking about this amount of force, I am just doing it. And I am moving my fingers to the proper keys (most of the time!) without having to think about it.
Even something as small as throwing a piece of paper into the trash is a wonder of engineering. I have to weigh the object. Figure ballistic trajectory. Flex my muscles the appropriate amount and let go at the proper spot. I guess more than just engineering but physics too.
I was walking with a cup of coffee and started thinking of how I had to counter the jar of my walking to prevent the coffee from spilling. It is just amazing.