It’s difficult to build devices that replicate the fluid, precise motion of humans, but that might change if we could pull a few (literal) strings. At least, that’s the idea behind “cable-driven” mechanisms in which running a string through an object generates streamlined movement across an object’s different parts. Take a robotic finger, for example: You could embed a cable through the palm to the fingertip of this object and then pull it to create a curling motion.