Yeah, there's definitely a lot more manipulation than they admit to. Around 1:50-2:00, a guy is turning a crank that flips the pages of another flipbook, but the pages keep turning at the same speed even while the speed of the crank changes dramatically.
Also, the apparent lack of regard for personal safety irks me a little. Wear some eye protection, dudes!
It's may have a flywheel to keep it consistent speed. It kind of looks like one at the top.
The fact that they were confident enough to not wear eye protection is one more thing that makes it impressive. I mean, certainly they have an insurance company that would want to see that they are being safe, right?
Also, the apparent lack of regard for personal safety irks me a little. Wear some eye protection, dudes!