Our joints are mechanical marvels that we take for granted every day. The range of motion, the strength and durability ... I will never look at going up and down the stairs quite the same way again.
While I seem to spend an increasing amount of time keeping my birth joints in working order, I have renewed incentive to continue and increase this practice. Not because I don't admire the bionic versions, but because I'd just as soon keep the slightly creaky but still-so-serviceable ones I have.
(Image: Wikipedia)