Here's how it works; when you push the saw down, fishing line gets reeled out in the back. A shaft turns, which is geared up so another shaft spins faster. Another strand of fishing line is attached to this shaft. When one strand of fishing line gets pulled out, another gets pulled in at a faster rate. One strand goes through the base and up into the saw, going through many wheels (yes, this was very hard to put through the wheels). There's also rubber bands that help reset everything.
Here are the instructions!
Here is the complete parts list, plus deconstruction pictures!
Here's the video: