when I did the resaerch for thisGR the Bowes museum website had a film of this exhibit working: now that seems to have gone teh way of all flesh with the re-design :-(

However, here is a picture of the swan.

Its fabulous in motion.

The sawn looks about him , sees small silver fish darting in the river( made from rods of twisted glass turning independently of each other), swooops down, catches one and eats it- all to the accompanient of lovely tinkly music( silver bells).