The Visible Cuckoo Clock 

As a kid, I had a Visible Man Anatomy Kit which was an educational toy with clear plastic skin so you could learn about the skeleton and internal organs of the human body. This two minute video is sort of like that, except that instead of the human body we are looking at a cuckoo clock. We see the weights hanging down and the pendulum swinging back and forth. Instead of the case, we see just the movement of the clock and if you look closely you can see the escape wheel (the beating heart of the clock) slowly turning. Then, mysteriously, about a minute in you can see and hear a lever drop, and then, less than a minute after that, all hell breaks loose. Then it's all over and the clock just ticks on.