If you watch the slow-mo part of the video at about 00:25 you can get a good idea of how it works.

The shackle is attached to a toothed, semi-circular hunk of metal. As you push the handle forward, a mechanism inside pushes the semi-circular hunk (that's the technical term) out from one side of the hook, and grabs and pulls it into the other side.

Pretty clever. It looks like the pieces have to be well aligned for it to work, so I wonder what happens after it gets knocked around a few times.

Dan <img src="http://www.traveltalkonline.com/forums/images/graemlins/Cheers.gif" alt="" />