Drop Rings "trick", vintage

Drop Rings, as advertised in a Western Puzzle Works catalog, item 12. Estimate over 100 yrs. old. This, technically, isn't really a puzzle, though it could be tricky to figure out how to make it work. When manipulated correctly, it produces an illusion of one ring water-falling down the chain from top to bottom. I managed to do it a few time, but I'm still not sure why it works the way it does. It's a very old trick. I imagine some blacksmith making chain-mail discovered this effect by accident.

The Western Puzzle Works catalog page is shown only as a reference. It is not part of this auction.

The chain is about 8" long, and each ring is 1/2" wide. I assume it's steel. 

US shipping is $5.85, international is $20.60, or shipping is free if you're winning one of the other auctions.