 This servo motor has a kind of super power. On top of basic control via the standard 3-pin connector, it has an additional wire for reading position of the internal potentiometer. Reading the voltage on this wire provides a reference to the servo's position, which can be used in code to improve accuracy so that the servo knows where it is. But beyond that, this lets us use the servo not just as a motor, but as a position sensor. By reading the servo position at regular intervals and saving those values to memory, we can record a sequence of movement. And once digitized, we can use that sequence of values to then reposition the servo again later, turning the internal potentiometer back to a previous position with each step, and effectively recreating the movement.